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Is it safe to use tap water for topping up in a pond this small?

the best way to top off a pond with "tap water" is to set your hose nozzle on fine spray. Spray the water high in the air over the pond. By the time the spray reaches the pond, the chlorine has evaporated. It is in a gaseous form.
I have a 4500 pond and have a float switch which activates when my water level drops about an inch. It turns on a fountain head in the center of the pond, which is piped to city water spraying it in the air before it goes in the pond. Chlorine will kill goldfish. I forgot and left a garden hose in a goldfish pond long enough to change water out complete. I lost all the goldfish I had in that pond. Leaving a hose in a pond is risky business, especially with a memory like mine!

Jim Warner
October 27, 1998

I have a similar size pond c/w goldfish , water hyacinths and something called (I think)water cabbages. It evaporates several inches a week with the water fall running. I just toss in the hose and fill it up. Our water contains lots of chlorine, so much in fact that they have to add ammonia as well just to keep the chlorine in. But it never hurts the goldfish. I believe it is because I never add more than about 10% at any time. In the spring, I clean out the pond and refill with new tap water. It takes about a week to "bloom" (turn grayish) then clears again about 3 days after that. Then I throw in the fish. The boffins at Environment Canada tell me the bloom is bacteria living off the ammonia, and once they have dealt with it, most of them die, but enough live on to purify the water almost immediately when I add a little more.

Jim Banner
September 10, 1998

The number of fish is important. This seems to be measured in inches of fish per gallon of water. When you get up to 1/2" of fish per gallon, that is a lot and you need pumping and filtration. But at 8 to 10 small goldfish, the aeration and cleansing provided by the waterfall, the snails, and the few plants, should be enough. If you top off relatively often, chemicals in your water will be diluted far more than if you wait for half the water to evaporate. Fish cannot take rapid temperature changes. The pond will get warm in the summer and topping off more frequently will reduce the chance of temperature shock. Fish need shelter from the sun and predators such as raccoons and egrets. The surface of our pond is about 85% covered with plants. You should try for about 50% which will help protect fish from birds but not from racoons. You have a milder winter than I do but could anyway consider whether to try to keep the fish over winter in such a small amount of water or just go buy more in the spring. If the pond freezes solid, your fish will die. Probably your pump will die, too, if it is submersible and you leave it in.

Phil Roos
September 11, 1998