The first weeks of a new pond

A freshly filled pond rarely looks like the photograph on day one. It is often cloudy, then green, then slowly clearer. That is a pond settling, not a pond failing. The useful skill in the first weeks is patience, and knowing which problems are normal and which need a hand.

Why the water goes cloudy, then green

Straight after filling, fine soil and dust stay suspended in the water. A little rain, a planted basket going in, or a pump stirring the bottom keeps it cloudy for a while. It settles as the pond calms down.

Green comes next. Algae arrive almost at once and grow fast in new water that has light and nutrients but not many plants yet to compete with them. The green pond water guide explains the difference between that floating green and the strands of blanketweed. In a new pond, both are common in the first season and both usually ease as plants take hold.

The Freshwater Habitats Trust puts pea-soup water down to excess nutrients, especially nitrate and phosphate, and lists tap water, soil or turf in the pond, bare soil nearby, and fish as common sources. That list is the checklist for a new pond too.

Keep the nutrients down from the start

• Fill with rainwater if you can. The Freshwater Habitats Trust's garden pond advice says most tapwater is not fit to use in a pond because of the nutrients in it, and suggests waiting for rain or collecting it in water butts. Topping up a pond covers the same choice once the pond is running.
• Keep soil and turf out. The same advice page warns that turf left in a pond adds a big dose of nutrients. Do not let the spoil heap wash back in.
• Use aquatic compost in baskets, not garden soil or multipurpose compost. The plants guide explains why.
• Do not reach for a bottle. A product that clears a new pond in a weekend is treating the symptom. Plants, shade and time treat the cause.

When to plant

The RHS wildlife pond guide says mid-spring to early summer is the best time for planting, once the water has warmed and plants are growing. A pond finished in autumn or winter, which is when the RHS suggests digging, can sit unplanted until then. It will still collect rain and the first visitors.

You do not have to plant at all. The Freshwater Habitats Trust says there is no need to plant a wildlife pond, and that plants will colonise it naturally if you are patient. If you do plant, they ask for local, native plants. The plants guide has the RHS list of plant jobs, and the warning about invasive species.

Do not bring in mud, water, plants or frogspawn from a friend's pond to "start it off". The RHS says moving them between ponds can introduce diseases, and invasive plants travel the same way.

Who turns up, and when

The RHS wildlife pond guide says pond skaters and diving beetles can arrive within a few days or weeks, and that damselflies and amphibians could easily be on the scene within the first year. That is the RHS's broad timescale for wildlife, not a test you need to pass. Some ponds fill faster, some slower, depending on what is nearby.

How to build a wildlife pond covers why a wildlife pond is left to colonise rather than stocked.

Why fish should wait

"New pond syndrome" is the phrase fish keepers use for the trouble fish run into when they go into a brand-new pond too early. In plain terms, fish produce waste from the first day, and a new pond, or a new filter, has not yet built up the bacteria that break that waste down. Waste can build up faster than the pond can deal with it. Overfeeding in the excitement of a new pond makes it worse.

The filter size guide covers the biological side of a filter and what the RHS says about how long its bacteria take to build. This page does not give a day count for your pond, because it depends on the pond, the filter, the temperature and the stocking. Ask the filter maker or an aquatic specialist when the system you have is ready, and how to tell.

Practical rules that do not need a number:

• Run the filter for the maker's recommended period before fish go in.
• Add a few fish, not the full stock at once.
• Feed lightly, and less than you think.
• Do not switch the filter off once fish depend on it.
• If fish look distressed, ask a vet or an aquatic specialist the same day. This site cannot diagnose fish.

If the pond is for wildlife, the simplest answer is no fish at all. The Freshwater Habitats Trust FAQ says fish usually overwhelm small garden ponds and eat smaller animals, including frog and newt tadpoles.

What to leave alone

• Do not empty and refill a cloudy or green new pond. You throw away the animals that have arrived and refill with the same nutrients.
• Do not keep adding tap water to "freshen" it.
• Do not net out every strand of algae in the first month. Pull blanketweed out by hand if it is choking the surface, and leave the rest.

Children and the new pond

A new pond is often surrounded by loose spoil, unfinished edges and an untidy beach. If young children use the garden, the RoSPA advice on the child safety page applies from the first day there is water in the hole.

How long will a new pond stay green?

There is no fixed time. It depends on light, nutrients, temperature and how quickly plants establish. Most new ponds improve as plants grow and as nutrients are used up. If the pond has fish and stays green, the filter and UV guides are the next step.

Should I add a bacteria product to a new pond?

That is a product decision, made on the maker's label, not a requirement. A wildlife pond with no fish does not need one. For a fish pond, ask the filter maker what their system needs.

Can I put frogspawn in a new pond?

The RHS advises against moving frogspawn between ponds, because it can introduce disease. Amphibians usually find a new pond on their own.