Q. We have a 55-gallon (208-liter) aquarium. It is filtered with a large canister filter (300 gallons [1135 liters] per hour) and an undergravel filter powered by two powerheads (each rated at 100 gallons [380 liters] per hour). There is also an air pump and airstones for additional aeration. The aquarium contains the following fancy goldfish: two black moors, one calico, one red cap veiltail, one chocolate oranda, one celestial, one celestial bubble eye and three bubble eyes.
Our aquarium conditions are as follows: The water temperature is usually 70 degrees Fahrenheit (21 degrees Celsius) but goes up to 80 degrees Fahrenheit (26 degrees Celsius) due to summer heat. The pH remains between 7.0 and 7.4. We have no chlorine in our water but it is very hard. Ammonia levels peaked and then declined, but the nitrite level remains at over 4.0 even though we do water changes and use activated carbon.
Is the temperature of 80 degrees Fahrenheit too high? Is the water too hard and, if so, should we soften it? What is the right pH for goldfish? Is our filtration system sufficient? The fins of some of our fish are splitting. Is this a disease or environmental? Sometimes our bubble eyes and celestials stay on the bottom of the aquarium. Is this a problem?
A. I really appreciate people who take the time to provide detailed information on their setup. It makes it possible to offer useful advice, rather than just guessing.
I know I am going to risk making some enemies starting off this way, but I have to tell you that you have too many goldfish in that 55-gallon aquarium. I would not keep any more than two or three mature goldfish in this setup — if you want healthy fish in a trouble-free environment. Relatively soon you are going to have significant problems with your aquarium due to overcrowding, and it is certain that the fish will not live out a normal life span in your current setup.
That said, let me get to your questions. Concerning the warmth of the water in summer, 80 degrees Fahrenheit is not a good temperature for goldfish because dissolved oxygen levels may drop too low. This is especially serious in an overcrowded aquarium. (You really didn’t think I was going to just drop the issue, did you?) However, your aquarium seems to have good aeration, so the problem may not be severe. You can cool the aquarium slightly by setting up a fan to blow across the open aquarium surface. Evaporative cooling works well. Just keep an eye on the water level.
I cannot comment on whether the well water is too hard, because “very hard” does not tell me much. Hobbyist test kits provide hardness measurements either in parts per million (ppm) of calcium carbonate or degrees of hardness (DH). Goldfish are fine in hardness levels up to around 200 ppm (12 DH). If the water turns out to be significantly harder, you can buy softening resins for your canister filter.
The mechanical, chemical and biological filtration system you describe is more than adequate for the task. The nitrite levels you report are very dangerous and are certainly part of the reason you see fin splitting and bottom sitting. Add 13 tablespoons of ordinary salt (or sea salt if you like) to the aquarium — 1 tablespoon for every 4 gallons of water — and the fish will be relieved of the nitrite stress. You can stop adding salt when the nitrite levels are unmeasurable.
I think it is also quite possible that the water currents in your aquarium may be too strong. This also contributes to fin splitting and stress. The canister filter plus two powerheads can really push a lot of water, and fancy goldfish were built to float and glide — not swim. I would find a way to drastically reduce aquarium currents. Given your canister filter, you only need to move about 55 gallons (208 liters) per hour through the undergravel filter, which will provide more than enough biological filtration.