Q. I have an 80-gallon freshwater aquarium. The pH is low (6.0 to 6.2), and the water tests very soft. I use well water that is delivered through copper pipes. The soft well water dissolves the copper, and so I suspect that I have a high copper content. Softwater species do very well — cardinal tetras, angelfish, cory cats, panda barbs — but I cannot keep others, such as tiger barbs, bettas, etc. Do you know of any way to test the copper content of my water? If copper is my problem, is there anything I can do about it?
A. Sufficient copper, especially in water with low pH, hardness or carbonate hardness, can indeed be toxic to fish. It’s even more toxic to invertebrates, and it can kill plants, too. But I suspect that your copper levels are lower than you think. Determining your copper level is easy. Just visit your local pet shop and look in the water test kit section. Copper test kits are commonly sold — though mainly to saltwater hobbyists. Copper sulfate is a common medication used in saltwater tanks, and test kits are necessary to be sure that the copper levels fall within a specific range. Too little is ineffective; too much kills the fish, along with the disease. If your dealer does not stock copper test kits, he can special order them, or you can buy them online.
The easiest solution to be rid of any copper in your waterlines is simply to run the water for a couple of minutes before using it. This should flush any water that was sitting in your pipes, absorbing copper. Alternately, aquarium shops sell copper-adsorbing resins (ADsorbtion is when something sticks to a surface) that can be introduced to your filter box. There are also liquid additives that bind with copper and other heavy metals to render them inactive.
Of more pressing worry to me is your low pH. Not only is copper more toxic in acidic water, but the acidic water itself can be a problem. In fact, when the pH is below 6.4, the helpful, nitrifying bacteria in your aquarium begin to stop functioning. This causes ammonia levels to rise in the form of ammonium ion. Ammonium ion is toxic to fish but becomes even more toxic if you do anything to increase your pH. The ammonium converts to ammonia, and that is highly toxic.
An excessively low pH can also be detrimental to many fish species. So what I would like to see you do is bump your pH and water hardness up a bit. I’d probably shoot for a pH of 6.8 to 7.0, and let the hardness rise with it as it sees fit. An easy way to do this is to add some dolomite or crushed coral to your gravel, or put it in a net media bag in your filter box. Your acidic water will dissolve a bit of these substances, which are largely made of calcium carbonate (CaCO3), releasing calcium and carbonates. The calcium increases water hardness. The carbonates increase carbonate hardness and (indirectly) the pH. This should eliminate the risk of ammonium buildup, and as a side benefit, will reduce any possible copper toxicity.
By the way, before you bump up your pH, run an ammonia test. If it is high, change all the water before adding crushed coral, or you could convert that ammonium to highly toxic ammonia.