Last year, I gave the guys, who have kindly provided me with a lifetime supply of emergency rotifers, a pair of clownfish that they successfully kept in a 10 gallon tank. Some months later, they decided that the fish needed a larger tank, so they moved them to a 20 gallon tank. Soon they were dead. The fish, not the guys. Recently, after months of leaving this tank alone, except to feed it to keep the biofilter alive, I brought them another pair of clownfish. This tank they went into was the same 20 gallon, had been cycled for months, was the right salinity, temperature, alkalinity, etc. The fish died within 3 days. These were pampered tank raised fish that I had kept for years in my system. So what killed them?
The tank had previously housed some frogs. I've never kept frogs, so I was wondering if something about keeping frogs could be toxic to saltwater fish. Any ideas?