Category: Ponds

Every pond loses some water. Sun, wind and a running waterfall all take their share, and on a hot, dry week the drop can look alarming. A leak is different: the level keeps falling at the same pace on mild days, and topping up becomes a daily job. The good news is that most leaks aren’t in the middle of the liner. They’re at the edges, in the waterfall or at a fitting, and you can find them with a bucket, a marker and a bit of patience.

Is it a leak or just evaporation?

Do a bucket test before you pull anything apart.

1. Set the bucket: sit a bucket on a pond shelf or a brick inside the pond so its rim is above the water.
2. Match the levels: fill the bucket with pond water until the level inside matches the pond outside.
3. Mark both: put a strip of tape or a pencil line at the water level inside the bucket, and another on a rock or the liner edge outside.
4. Run as normal: leave the pump on for 24 hours.
5. Compare: if both have dropped about the same amount, that’s evaporation. If the pond has dropped noticeably more than the bucket, you’ve got a leak.

Repeat it if the weather was wild that day. A strong hot wind can fool a single test.

Where do pond leaks usually hide?

Start with the parts that move water, not the pond itself. The liner tends to be the last thing at fault, even though it’s the first thing people suspect.

• The waterfall or stream: water splashing over the side, running under a rock that’s shifted, or escaping where the liner under the stream wasn’t folded up high enough at the edges.
• Low spots in the edge: the ground settles, an edging stone sinks, and the liner rim ends up below the waterline in one corner.
• Wicking: soil, mulch or plant roots touching the water and the ground outside the liner draw water out like a candle wick.
• Fittings and hoses: bulkhead seals, filter connections and the hose clamps at the pump outlet. A slow drip from an external filter adds up over a week.
• The liner itself: punctures from sharp rocks, roots or a dog’s claws, or a crack in a preformed shell.

Finding the leak, step by step

Step 1: Turn the pump off

Switch off the pump and let the pond sit for a day. If the level holds steady with the pump off, the leak is in the plumbing, the filter or the waterfall, not the pond.

If you keep fish, don’t leave them without circulation for long in warm weather. Add an air stone while you test. Our guide on whether your pond needs an aerator covers why oxygen drops quickly in still, warm water.

Step 2: Check the water feature run

With the pump back on, walk the full length of the waterfall or stream. Look for damp soil beside the rocks, a trickle going sideways off a lip, or water disappearing behind a stone. Lift the liner edge along the stream where you can. It should be turned up well above the flow line on both sides.

Step 3: Let the pond find its own level

If the pond still drops with the pump off, stop topping it up. Let it fall until it stops. The leak sits at or just above the line where it settles. Run your fingers slowly around the liner at that height and look for a hole, a split, a fold that’s lifted, or soil touching the water.

Step 4: Use milk or food dye to pinpoint it

On a still day, squeeze a few drops of milk or a pond-safe dye near a suspect spot with the pump off. If there’s a hole, the cloud drifts towards it and gets drawn in.

How do you fix it?

The repair depends on what the pond is made of. If you’re not sure what you’ve got, our breakdown of EPDM, preformed and concrete pond liners will help you tell them apart.

• EPDM rubber liner: lower the water below the hole, clean and dry the area, apply EPDM primer, then press on a self-adhesive EPDM patch and roll it firmly from the centre out. Give the patch a good margin past the damage on every side.
• PVC liner: use a PVC repair kit and glue made for liners. PVC gets stiff and brittle with age, so if it’s cracking in several places, budget for a new liner.
• Preformed shell: small cracks in fibreglass can be repaired with a fibreglass kit. Cracked plastic shells rarely hold a lasting repair and are usually cheaper to replace.
• Concrete: clean out hairline cracks, fill with a sealant rated safe for fish, and follow the maker’s cure time before refilling.
• Edges and wicking: lift sunken stones and pack soil under the liner rim to raise it, trim back roots and pull mulch away so nothing bridges the liner edge.

For bigger leaks that mean draining the pond, move the fish into a shaded tub of their own pond water with an air stone before you start. If the job turns into a rebuild, our guide on building a garden pond covers underlay and edging so the new liner doesn’t end up with the same problem.

Topping up while you sort it out

Until the leak’s fixed, you’ll be adding water, and tap water isn’t ideal for fish. Town water is treated with chlorine or chloramine, depending on your supplier, so use a dechlorinator if you’re topping up from the hose.

Rainwater from a clean tank avoids those disinfectants altogether. If you’re in Queensland and want one installed and hooked up properly, Creek to Coast Plumbing handles rainwater tank installations.

After any big top-up or repair, check your water over the next few days. Our guide to testing pond water at home walks through what to look for.

Your fish are hanging at the surface, gulping. The water looks fine, maybe a bit green. What’s actually wrong? A ten-minute water test at the pond’s edge is the place to start. The three numbers that matter most are ammonia, nitrite and pH.

You don’t need a chemistry background. You need to know what each number is telling you, how to take a sample that isn’t misleading, and what to do when a reading comes back wrong.

Why test water that looks clear?

Because the stuff that hurts fish is invisible. Fish waste, uneaten food and rotting leaves all break down into ammonia. In a healthy pond, bacteria living in your filter and on every surface turn that ammonia into nitrite, then turn nitrite into nitrate. Ammonia and nitrite are both toxic to fish. Nitrate is far less harmful and gets taken up by plants.

When that chain breaks, ammonia or nitrite builds up while the water still looks perfectly clear. Clarity tells you about particles and algae, not chemistry.

Strips or liquid kit?

• Test strips: quick and easy, dip and compare colours. Good for a fast weekly check, but they’re less precise and they go off quickly once the tub is opened and damp gets in.
• Liquid reagent kits: drops into a vial of pond water, wait, compare against a card. Slower, but more accurate.

Whichever you use, check the expiry date. Old reagents give confidently wrong answers, which is worse than no answer at all.

How to take a test properly, step by step

1. Pick a consistent time: pH moves through the day, so test at roughly the same time each time you check. Early morning gives you the low point.
2. Sample from the right spot: dip the vial about elbow-deep, away from the pump outlet, the waterfall and any spot where you’ve just topped up with the hose.
3. Rinse first: swill the vial with pond water and tip it out before filling.
4. Follow the kit exactly: the number of drops, the shaking and the waiting time all matter.
5. Read in daylight: hold the vial against the white part of the card in natural light, not under a yellow patio globe.
6. Write it down: date, time, reading, and anything you changed recently.

What the numbers mean

Ammonia

The target is zero, or as close to it as your kit can show. Any detectable ammonia means waste is being produced faster than your bacteria can process it. The usual causes: too many fish, too much food, or a filter that’s undersized or over-cleaned. Ammonia is also more toxic in warm water and at higher pH, so a reading that’s tolerable in winter can be dangerous on a hot summer afternoon.

Nitrite

Also zero. Nitrite shows up when the first lot of bacteria is working but the second lot hasn’t caught up. You’ll see it most in new ponds that are still establishing and after a filter has been over-cleaned. Fish with nitrite poisoning often look sluggish and gasp even when the water is well oxygenated.

pH

Most pond fish and plants are comfortable somewhere around 7 to 8.5. The exact figure matters less than stability. A pond that sits at 7.8 every morning is in better shape than one that swings from 7 to 9 between dawn and late afternoon. Those daily swings happen because plants and algae use up carbon dioxide during the day, pushing pH up, then release it overnight.

If your kit also measures KH (carbonate hardness), test that too. KH is the water’s buffer. When it runs low, pH can crash suddenly, often after heavy rain. New concrete or mortar does the opposite, leaching lime and pushing pH high until it’s sealed or cured.

A reading’s off. Now what?

• Ammonia or nitrite above zero: stop feeding for a few days. Do a partial water change, a common rule of thumb is around 10 to 20 per cent, and retest the next day.
• Treat your top-up water: many mains supplies are disinfected with chlorine or chloramine. Check with your local water utility, and use a dechlorinator rated for both.
• Look at the filter: if you rinsed the media under the tap, you’ve likely killed off the bacteria. Rinse it in a bucket of pond water instead. Our guide to pond filtration and UV clarifiers covers sizing and cleaning in more detail.
• Get oxygen in: stressed fish need it most, and warm water holds less of it. An air stone or a bit more surface movement buys time while you fix the cause. See whether your pond needs an aerator.
• pH swinging or low: check KH first. Raising KH steadily with a pond buffer is safer than dosing pH up or down directly, which tends to overshoot.

Don’t fix everything at once. Big, sudden changes stress fish more than a slightly off reading does. Make one change, wait, retest.

How often should you test?

For a new pond, test weekly for the first couple of months while the bacteria establish, and any time fish behave oddly. Once a pond has been stable for a season, monthly is usually enough, plus a check after heavy rain, a hot spell, adding new fish or cleaning the filter.

Stocking levels and feeding have the biggest influence on what your tests show. If you’re keeping goldfish or koi, our fish pond basics explains how much load a pond can handle. Plenty of healthy planting helps too, by soaking up nitrate before algae can use it. The aquatic plants guide is a good place to start.

Keep the kit dry and shaded, with the notebook beside it, and you’ll often spot trouble before your fish do.

A frog-friendly pond is shallow at the edges, thick with native plants, free of fish and left mostly alone. Get those four things right and local frogs will usually find it on their own. You don’t stock a frog pond. You build the conditions and wait.

That waiting is the hard part for most people. Frogs might turn up in the first warm, wet spell, or it might take a season or two. Either way, don’t go and fetch them from somewhere else. More on why below.

What makes a pond suit frogs rather than fish?

Frogs need to get in and out of the water easily, lay eggs where nothing eats them, and shelter close by. A typical ornamental pond fails on all three. It has steep sides, goldfish that hoover up eggs and tadpoles, and a bare paved edge with nowhere to hide.

• Shallow, sloping edges: at least one side should run out like a beach, so frogs and tadpoles can move from deep water to damp ground.
• One deeper spot: deep enough that the pond won’t dry out or cook in a hot week, which gives tadpoles somewhere to retreat.
• No fish: goldfish, koi and most native fish will eat eggs and tadpoles. A frog pond and a fish pond are two different projects.
• Cover all round: rocks, logs, leaf litter and dense groundcovers near the water give adult frogs somewhere cool and damp to sit out the day.

If you’re starting from scratch, our step-by-step guide to building a garden pond covers digging and shelving. For a frog pond, just make the shelves wider and the slope gentler than you would for fish.

Where should it go in the yard?

Put it somewhere with a mix of sun and shade. Full sun all day heats a shallow pond fast and feeds algae. Deep shade under a big tree means cold water and a constant drop of leaves.

Keep it away from where you spray. Frogs take in water and chemicals through their skin, so a pond next to a sprayed lawn or a rose bed that gets regular treatments is a poor bet. Run your downpipes and paving runoff away from it too.

Quieter corners work better than the spot right outside the back door. Frogs will put up with people, but they won’t put up with a dog that wades in every afternoon.

Which liner and edge work best?

A flexible liner is usually the easiest way to get a long, gentle slope. Preformed shells tend to have steep walls and narrow ledges, which is the opposite of what frogs want. Our comparison of EPDM, preformed and concrete pond liners goes through the trade-offs in detail.

Once the liner is in, cover the shallow end with soil, gravel and flat stones so frogs have grip. Bare liner is slippery, and a tadpole that’s turning into a frog can’t climb a slick plastic wall.

What should you plant?

Plant in layers: submerged plants for oxygen and tadpole cover, rushes and sedges along the margins for egg laying and shade, and dense groundcovers on the bank. Plants also soak up nutrients that would otherwise feed algae.

Go local wherever you can. A native nursery near you will know which rushes, sedges and water plants grow naturally in your area. Be wary of cheap pond plants bought online, because some popular water plants are declared weeds in parts of Australia and can choke a waterway if they escape. Our guide to choosing aquatic plants for a balanced pond explains what each layer does.

Do you need a pump in a frog pond?

Not necessarily. Plenty of good frog ponds are still water with heavy planting. Frogs generally prefer calm water for laying, so a strong waterfall or a jet fountain works against you.

If you want some movement, keep it gentle and put a guard or sponge pre-filter over the intake. An unguarded intake will pull in tadpoles. A small, low-flow solar pump trickling over a stone is often plenty. Any mains-powered pump needs a properly installed outdoor power point, and new fixed wiring is a job for a licensed electrician.

What about mosquitoes, algae and top-ups?

A balanced pond with frogs, dragonfly larvae and other aquatic insects usually keeps mosquito numbers down. Don’t add mosquitofish (gambusia). It’s an introduced pest that preys on frog eggs and tadpoles.

Skip chemical algae treatments. Shade, planting and patience fix green water more safely. Top up with rainwater where you can. Tap water carries chlorine or chloramine, so if you must use it, add small amounts at a time.

Can you move frogs or tadpoles in yourself?

Don’t. Moving frogs, spawn or tadpoles between sites can spread disease, including the chytrid fungus that has hit frog populations hard. Taking native frogs or tadpoles from the wild is also regulated in most states. If you’re unsure what’s allowed, check with your state environment or wildlife agency before you touch anything.

In parts of Queensland, northern New South Wales and northern Australia, cane toads will use a garden pond too. Toad eggs come in long strings, while native frogs usually lay clumps or floating foam. Native frogs get mistaken for toads all the time, so confirm the identification using your state or local council’s guidance before removing anything.

Is a frog pond safe with kids around?

Shallow edges help, but any water is a drowning risk for a toddler. Rules on barriers around garden ponds vary by state and council, so check locally. Our backyard pond safety guide goes through fencing, depth and covers.

Build it, plant it, leave the fish out and resist the urge to tidy. The first time you hear a chorus from your own pond on a warm night, you’ll know it worked.

If your fish are hanging at the surface gulping at first light, or crowding around the waterfall where the water splashes in, they’re short of oxygen. That’s the clearest sign a pond needs aeration. Most small, well-planted ponds with a decent pump get by without a dedicated aerator. Ponds with a good load of fish, deep still water or a hot summer ahead usually don’t.

Why is oxygen lowest just before sunrise?

Pond plants and algae make oxygen during the day and use it up at night. Fish, bacteria in the filter and rotting leaves on the bottom use oxygen around the clock. By about dawn the pond has spent the whole night drawing down its supply with nothing topping it up, so that’s when it bottoms out.

Warm water makes it worse. It holds less dissolved oxygen than cool water, and fish breathe harder when they’re warm. A run of hot, still, humid nights in January is the classic time for a fish loss. Heavy cloud for a few days in a row does the same thing, because the plants aren’t photosynthesising much during the day either.

Watch for these signs:

• Gasping at the surface: fish nosing the top of the water early in the morning, then settling once the sun’s up.
• Crowding the waterfall or outlet: they go where the water is being mixed with air.
• Sluggish feeding: fish that normally rush the food ignore it on warm mornings.
• A green bloom that suddenly clears: a big algae die-off consumes a lot of oxygen as it breaks down, and losses often follow a few days later.
• A rotten egg smell from the bottom: that’s sludge breaking down without oxygen, and it’s a sign the deep water is stagnant.

Doesn’t my pond pump already add oxygen?

It does, but only where the water meets the air. Oxygen gets into a pond through the surface, so anything that breaks or turns over the surface helps: a waterfall, a fountain, a stream return. A pump on its own, pushing water through a filter and straight back in under the surface, adds very little.

The other limit is depth. A waterfall stirs the top layer well, but in a pond deeper than about a metre the bottom water can sit still for weeks. That’s where the sludge is, and that’s where oxygen runs out first. If you’ve sized your pump for turnover (our guide to sizing a pond pump covers that), it may still leave the deep end barely moving.

What does an air pump actually do?

A pond air pump sits outside the water and pushes air down a thin hose to an air stone or diffuser on the bottom. The bubbles themselves add a little oxygen, but their real job is lifting bottom water to the surface. That circulation is what matters. The whole pond gets turned over slowly, the deep water gets its turn at the surface, and the bottom stops going stagnant.

Air pumps are cheap to run because they’re moving air, not water. A small diaphragm air pump typically draws a fraction of the power of a water pump. They’re quiet if mounted on something soft and kept out of the sun.

When is an aerator worth adding?

We’d put one in if any of these are true:

• You keep koi or goldfish in decent numbers: fish are the biggest oxygen users, and koi get big. Our koi and fish pond basics cover sensible stocking.
• The pond is deep with no bottom drain: a diffuser on the floor is the cheapest fix for dead water down low.
• There’s no waterfall or fountain: a flat, still surface takes in very little oxygen.
• You’ve lost fish on hot nights before: that’s the pond telling you.
• Your main pump runs on solar: unless it has a battery, it stops when the sun goes, which is exactly when oxygen drops. See our notes on what solar pond pumps can and can’t do.

A shallow frog pond with plenty of plants and no fish rarely needs one. The plants and the big surface area do most of the work.

How to set one up properly

Put the diffuser in the deepest part of the pond, raised a little off the floor on a brick or flat stone so it doesn’t stir sludge into the water column. One good diffuser does more than several small ones scattered around.

Mount the pump above the waterline, somewhere shaded and dry. If it sits below water level and the power cuts out, water can siphon back down the hose into the pump. A check valve in the line stops that, and they cost a few dollars.

Run it overnight at a minimum. Plenty of owners run it 24 hours through summer. Through winter, move the diffuser up off the bottom, about halfway up, so you aren’t mixing the warmer deep water through the whole pond. There’s more on cold-weather settings in our winter pond care guide.

Powering it safely

Most air pumps plug into a standard outdoor power point. That outlet needs to be weatherproof, on an RCD-protected circuit, and kept well clear of splash. If you don’t already have a suitable outlet near the pond, installing one is licensed electrician work in every state and territory. It isn’t a DIY job.

Don’t run an extension lead across the lawn as a permanent setup. Leads get cut by mowers and joins end up sitting in puddles.

The short answer

If the pond has fish, is deeper than your arm, or relies on a solar pump, an air pump is cheap insurance and worth fitting before summer, not after the first loss. If it’s a shallow, planted pond with a lively waterfall and a light fish load, you can probably skip it and keep an eye on the fish on hot mornings instead.

Short version: spring is for waking the pond up, summer is for keeping the water topped up and full of oxygen, autumn is for keeping leaves out, and winter is for leaving it alone. Here is the year laid out season by season, using southern hemisphere months.

Read the months as a guide, not a timetable. A pond in Hobart and a pond in Townsville run on very different clocks, and up north the wet and the dry matter more than four seasons do. Go by what your water is doing.

Spring (September to November): the wake up

This is the busiest stretch of the pond year. The water is warming, the fish are getting hungry, and algae is waking up at the same time.

• Clear the bottom: Scoop out the sludge and rotting leaves that settled over winter. Take most of it, not all of it. A thin layer does no harm, and stripping the pond bare knocks the whole system about.
• Service the pump and filter: Pull the pump, clear the intake and check the impeller turns freely. Rinse filter media in a bucket of pond water, never under the tap. Chlorinated tap water kills the good bacteria your filter depends on.
• Bring feeding back slowly: Start small once the fish are active and coming up for food, and build up over a few weeks.
• Divide and repot plants: Waterlilies and marginals that have outgrown their pots can be split now, while they are pushing new growth. Our guide to choosing aquatic plants for a pond covers what goes where.

Expect a green flush in spring. Warm water, strong sun and plants with too little leaf to shade the surface set it up, and it usually settles as they fill out. If it doesn’t, the steps for keeping algae under control are the next stop, and reaching for chemicals first isn’t one of them.

Summer (December to February): water and oxygen

Summer trouble is rarely dramatic. It’s the slow stuff: the level dropping, the water warming, oxygen falling away overnight.

Topping up

You will lose water to evaporation in hot, windy weeks, and in a shallow pond the same drop is a bigger share of the water. Top up little and often rather than refilling a big drop in one go. If you use town water, add a water conditioner made for ponds to neutralise the chlorine or chloramine. Rainwater from a tank is gentler if you have it. Before you run a hose, check the current rules with your local water authority. Some restrictions cover ponds and water features, and they differ from one authority to the next.

Keeping oxygen up

Warm water holds less oxygen than cool water, and plants use oxygen overnight instead of making it. That’s why fish gasping at the surface first thing in the morning is a summer sight. Keep the pump running around the clock through the hot months. A waterfall, fountain or air stone adds oxygen as the water breaks the surface. If fish are gasping at dawn, add more aeration straight away and cut back on feeding.

Shade and feeding

Aim for plants to cover a good share of the surface by midsummer. Lily pads and floating plants shade the water, keep it cooler and starve algae of light. Feed what the fish clear in a few minutes and net out anything left over. Uneaten food rots, and in warm water that goes bad fast.

Autumn (March to May): beat the leaves

Autumn’s job is simple: stop organic matter getting into the pond before winter locks it in there. Every leaf that sinks and rots over the cold months turns into sludge and nutrients that feed next spring’s algae.

• Net the pond: If you’re near deciduous trees, a fine net stretched over the surface for a few weeks saves hours of scooping later. Keep it taut and clear of the water so birds and lizards don’t get tangled.
• Cut back plants: Trim marginals as they yellow and pull dying lily leaves before they sink. Anything that dies back will end up on the bottom if you leave it.
• Ease off feeding: As the water cools, fish need less. Cut portions and frequency down gradually as activity slows.
• Give the filter a clean: Do a proper clean now, rinsed in pond water, so it isn’t clogged when you want to leave it alone over winter.

Autumn is a good time to check the power side too. Look over leads for cracks and make sure the pump runs through a safety switch (RCD). If you need a new outdoor power point near the pond, that is a job for a licensed electrician, not a weekend project.

Winter (June to August): leave it be

In most of the country, winter pond care is mostly not interfering. Keep the pump ticking over, cut feeding right back or stop once the fish go quiet, and keep leaves out. Frost country is the exception, and the details for that, including when shutting down a pump makes sense, are in our guide to caring for ponds and pumps through the cold months.

The classic winter mistake is a big clean-out on a sunny July day. With the fish sluggish and the filter bacteria barely active, it does more harm than good.

If you only remember four things

• Spring: clean out gently, service the pump and filter, bring feeding back slowly.
• Summer: top up little and often, keep the water moving day and night, shade the surface.
• Autumn: net out the leaves, cut back dying growth, clean the filter.
• Winter: feed little or nothing, keep the leaves out and save the big jobs for spring.

A pond without plants is just a hole full of water waiting to turn green. Plants are not decoration you add once the hard landscaping is done. They are the part of the system that keeps the water clear, keeps the fish happy and does most of the work that a filter would otherwise have to do on its own.

Why plants do more than look good

Every pond has a nutrient load coming into it: fish waste, decaying leaves, whatever runoff washes in off the surrounding garden. Algae thrives on exactly that load, and if nothing else is competing for it, algae wins. Plants take up those same nutrients as they grow, which starves the algae of what it needs.

On top of that, plants shade the water surface and cut how much direct sun hits it, which slows algae growth even further. Submerged plants also pump oxygen into the water during daylight hours, which fish and the beneficial bacteria in your filter both rely on. A well-planted pond genuinely needs less mechanical filtration to stay clear than a bare one.

The three plant types and what each one is for

Every healthy pond mixes plants from three broad categories, and each does a different job.

• Submerged plants: these grow fully underwater, oxygenating the water and soaking up nutrients directly from it. They are the real algae fighters in the mix and are often sold in bunches to be weighted and dropped straight to the bottom.
• Marginal plants: these sit in shallow water at the pond’s edge, roots underwater and foliage above it. Reeds, rushes and irises fall into this group. They soften the hard edge of the pond, give small fish somewhere to shelter, and filter water as it moves past their root systems.
• Floating plants: these sit on the surface with roots trailing below, taking up nutrients straight from the water column while their leaves shade everything underneath. This is your fastest way to knock back algae in a pond that has gone green, because they compete directly with it for light and food.

Get a mix of all three and you are covering oxygenation, shade and filtration at the same time, rather than leaning on one plant type to do everything.

How much is actually enough

You do not need to fill the pond with plants to get the benefit. As a general guide, aim for somewhere around a third of the water surface covered by floating and marginal foliage once everything has grown in, with a healthy scattering of submerged plants through the deeper water. That is a rough target to work towards over a season, not a number to hit on planting day, because most pond plants spread a long way from where you first put them.

Underplant to start with. It is far easier to add more later than to claw back a pond that has gone completely over to lily pads and rushes within a year.

Planting depths and how to actually plant them

Most pond plants are easiest to manage in planting baskets rather than straight into the pond floor. A basket lined with hessian and filled with proper aquatic planting media keeps the roots contained, makes dividing the plant later far simpler, and stops soil clouding the water every time you disturb it.

Depth matters more than people expect. Marginals generally want their crowns just at or barely below the surface, sitting on a shelf near the pond edge. Water lilies and other deeper-water plants need their baskets lowered gradually as they grow, starting shallow when the plant is small and moving deeper as the leaves reach the surface. Submerged plants can usually go straight to the bottom, weighted down until their roots take hold.

If your pond does not have built-in planting shelves at different depths, bricks or stacked pavers under a basket do the same job and let you fine-tune the height as the plant establishes.

Keeping plants and fish working together

Fish and plants generally get on well, with a couple of things worth knowing. Some fish, koi in particular, will happily dig up and eat softer plants, so if you are running a koi pond, lean harder on tougher marginals and protect any water lilies with a bit of wire mesh around the basket until they are established.

Overplanting is the other trap, particularly with fast spreaders. A pond that is more than half covered in floating foliage can start blocking too much oxygen exchange at the surface, which works against the fish you are trying to look after. If you are ever unsure whether a particular plant is appropriate to grow or release in your area, check your state or council weed list before buying, since a few common pond plants are restricted in parts of Australia.

Seasonal upkeep and dividing overgrown plants

Plants slow right down over the cooler months and pick back up as the water warms in spring, which is the best time to do most of the work. Marginals and water lilies benefit from being lifted, divided and repotted every couple of years once they have filled their basket, both to keep them healthy and to stop them taking over the pond.

Trim back dying foliage as the seasons turn rather than leaving it to break down in the water, since decaying plant matter feeds algae the same way fish waste does. A quick tidy-up each season keeps the whole system doing its job instead of working against it.

If you are still setting the pond up, our step-by-step guide to building a garden pond covers the build itself, and our guide to pond filtration and UV clarifiers goes deeper into the mechanical side of keeping the water clear. Both link back to our full guide to water in the Australian garden.

Ask most people why the fish in their backyard pond died and they will blame a disease. Nine times out of ten it was not a bug at all. It was the water. Get the water right and healthy fish largely look after themselves, so that is where a beginner should put nearly all their attention.

Here is what actually keeps koi and goldfish alive and well in an Australian backyard: enough water, enough oxygen, a filter that has had time to mature, sensible feeding, and a bit of protection from summer heat and hungry birds. Work through those in order and you will dodge the mistakes that catch nearly everyone starting out.

Give them more water than you think they need

Fish are far more forgiving in a big body of water than a small one, because a larger volume dilutes waste and holds a steadier temperature. A tiny ornamental pond heats up fast on a hot day and crashes cold on a still night, and those swings stress fish badly.

As a rough guide rather than a hard rule, keep your stocking light. Beginners almost always want too many fish too soon, and an overstocked pond is the most common reason water goes bad. Koi in particular grow big and live for decades, so a handful of little ones today can become a serious load in a couple of years. Depth helps too: a deeper section gives fish somewhere cooler in a heatwave and steadier through winter. If you are still planning, our step-by-step guide to building a garden pond covers sizing and depth before you dig.

Oxygen: the thing beginners forget

Fish breathe dissolved oxygen, and warm water holds a lot less of it than cool water, which is why gasping at the surface on a hot, still morning is such a common panic. The fix is movement. Anything that breaks the surface, a small fountain, a waterfall, or an air pump with an airstone, pulls oxygen into the water.

A few things worth knowing about aeration:

• Run it through the night in summer: plants and algae consume oxygen after dark, so the lowest oxygen of the day is usually just before dawn.
• Surface agitation beats depth: gas exchange happens where water meets air, so a gentle ripple across the top does more than a jet firing into the deep.
• Get the power done properly: any pump or aerator wired to a fixed outdoor power point must be connected by a licensed electrician. Plug-in and low-voltage solar kits are fine to set up yourself, but mains work is not a DIY job.

The nitrogen cycle, in plain English

This is the bit that quietly kills more fish than anything else. Fish produce ammonia through their waste and gills, and ammonia is toxic. In a healthy pond, colonies of beneficial bacteria living in your filter convert that ammonia into nitrite (still toxic) and then into nitrate (far less harmful, and taken up by plants).

The catch is that a brand new pond has none of those bacteria yet. Fill a pond on Saturday and drop fish in on Sunday, and the ammonia has nowhere to go. Let a new pond run for several weeks so the filter can mature before you add stock, add fish slowly, and pick up a simple water test kit so you are reading the water rather than guessing. The filter is the engine room of the whole thing, so it is worth getting right. Our guide to pond filtration and UV clarifiers covers how to match one to your pond.

Feed less, and never in the cold

Overfeeding is the fast track to green, smelly water, because uneaten food rots and spikes ammonia. The old rule holds up: only give them what they will clean up in a couple of minutes, and once a day is plenty for most backyard ponds. Fish are cold-blooded too, so as the water cools through autumn their metabolism slows right down and they can barely digest. Once it is genuinely cold, ease off and then stop feeding over winter, or you are just leaving rotting food in a pond that can least handle it.

Surviving an Australian summer

Heat is the big seasonal risk. Hot water holds less oxygen, evaporates faster, and pushes fish to their limits. A few sensible moves take the sting out of it:

• Throw some shade: floating plants like water lilies, or a shade sail over part of the pond, keep the water cooler and give fish somewhere to hide.
• Top up gently: evaporation concentrates everything in the water, so keep the level up, and if you top up with town water let it stand or treat it for chlorine first.
• Beat the birds: herons, kookaburras and the neighbour’s cat all fancy a feed, so a deeper zone, overhanging plants or netting gives fish a fighting chance.

Reading the warning signs

Fish tell you when something is off, usually well before it turns into a disaster. Watch for gasping at the surface, fins clamped tight against the body, flashing (rubbing against rocks), or fish going off their food and sitting listless on the bottom. The first response is nearly always the same: test the water and improve the oxygen. A partial water change and more aeration fixes a surprising number of problems.

If fish stay sick after you have sorted the water, or you are seeing sores, ulcers or clear signs of parasites, get proper advice rather than throwing random medications at the pond. An aquatic vet or a specialist aquarium supplier can identify what you are dealing with and dose it correctly. Guessing at treatments does more harm than good.

Plenty of water, steady oxygen, a mature filter, restrained feeding and a little seasonal common sense will carry a backyard pond full of healthy fish for years. For the bigger picture on pumps, ponds and water features around the garden, start with our complete guide to water in the Australian garden.