We are down to one fish in the aquaponics experiment out of the three we started with.  Here’s an excerpt of Dillon’s paper on the topic:
I started the project with three fish. My fish are a chocolate oranda named Shadow, a redcap oranda named Ron, and a butterfly tail goldfish named Shy. [A bunch of research paper deleted here.] I had a number of problems with the fish part of the experiment, though I was on the lookout for these problems thanks to my reading. I first had a pH problem, because the pH of the water would spike and get too high for the fish, and we had to lower the pH by using a product called pH down. Then I had a temperature problem, and the water was too cold, so we got an aquarium heater. Finally, I had an oxygen problem, which I realized because the fish were gasping for air at the top of the tank. We got an oxidizer for the fish to solve this problem. We lost two fish during the experiment probably due to these problems, or the fluctuations in these elements. The book I was working from, Aquaponic Gardening, told me to expect this and suggested to gardeners to start their cycle with goldfish rather than tilapia or perch because you often lose fish when you are starting up your system before all of the levels are regular enough and stable.
So, Shy and Ron are no longer with us. What the writing above doesn’t really tell you is the level of hysteria that my kids felt at the death of Shy. They kept it together a bit more when the second one, Ron, died. (Poor Ron Weasley, I think it wasn’t as sad because they didn’t really notice he was sick, Shy was clearly not doing well for a while.) And Shadow is looking a little shady. But we’re testing everything and the water seems to be habitable for the fish, with an appropriate pH, ammonia, nitrites, and nitrates. I’ve had a number of (even long-lived) goldfish in my life, and never kept them in such luxury or cared about the chemicals in the water, which often wasn’t changed particularly regularly.  Did we just get lemons in the goldfish department? It’s only been six weeks – I thought for sure we could keep at least one alive for a couple of months. Thoughts?
