My friends red glo fish, which he has had for about 3 weeks, is not swimming like he used to. The fish just stays in one spot and will not eat. His tank is cycled, so that is not the problem. I looked at the fish and his fins are not clamped and the fish doesn't look weird. Other fish look fine and eat. His other fish are doing fine, but he is having a problem with the glo fish and the yellow one just died not too long ago.
I was just wondering if something was wrong. He does water changes and his tank is cycled.
Over feeding is a common problem, and it will affect water quality even in an aquarium with a working nitrogen cycle. If ammonia and nitrite measure zero, water quality is not an issue.
Glow fish are genetically modified zebra Danios, and sometimes those modifications introduce weaknesses. Zebra fish also tend to be very social and are more comfortable in a shoal of at least six. Does the fish have any symptoms beyond the behavioral issues?