I moved into a property about 3 months ago which had a small pond in the back garden. The approximate size of the pond is about 4ft x 3ft x 2ft. It had no filter, pump, or plants at the time, just the butyl liner in the hole in the ground and a disused waterfall feature. My wife was quite keen to have some fish so we put in about 20 small goldfish that we bought from a local garden centre with fish pond supplies. We also added a pump (1000 litres per hour) which I connected to the waterfall feature and sometimes switch over to a fountain. The pump does seem very underpowered as when I connect it to the waterfall there is little more than a dribble of water returning at the bottom to the main pond. We do leave the pump on 24/7. The fish have been fine for a couple of months, feeding well and seem healthy. However, now one or two of the fish have died and the others don’t seem well at all.They seem to congregate at the top near the edge of the pond as if they are gasping for air. I know that sounds daft as they are fish and don’t need air??? I would like to sort the problem out but don’t know what to buy. Do I need a filter? Do I need a bigger pump? Do I need plants (I have none). I have added two treatments to the pond, both Tetra products. One I add when I top up the water level with tap water which isn’t very often, and the other is an algae clear additive. I do live in the UK so temperature is dropping a bit now were approaching Winter….is that a factor? Any advice gratefully received… Regards Ed.

Well Ed, the good news is that you don’t need t spend any more money on gadgets from the fish pond supplies shop! Oh, is that bad news sorry!

You have too many fish for a small garden pond of that size, and as they grow they are demanding more oxygen than the surface of the pond can provide. Adding some plants may help, and will get rid of the need to add algicide which doesn’t seem like a very good idea anyway. But unfortunately, as the fish grow, with that number in the pond then there will be deaths until a sustainable population of about half a dozen is reached. It will usually be the largest fish that die first. So if you can take some of the fish out and give them away to somebody who has a a much larger pond, that would be a great idea. You could also see if teh fish pond supplies shop will take them back.

Ideally there would be such a large reservoir of rainwater collected from a big roof area into huge storage containers that tap water would never be necessary, but that isn’t practical with the setup I have here at the moment. Rainwater is generally preferable to tap water because the tap water contains a background level of nitrate which is not good for the animal and small insect life in the pond, also the PH of tap water is treated to be less corrosive to pipework whereas the pond life is happier, I think, with the slightly more acidic rainwater.

Not only that but also tap water has been expensively treated to make it suitable as drinking water for humans. Its really a waste to use it for other purposes unless absolutely necessary.

Another way to cut down on the need to top up any small pond is to cut back the vegetation somewhat. Water irises once they have flowered can be taken right back to near the surface level, although then you will miss out on the spectacular seed heads.

Irises in the small pond - cut back to save water?