False Neons Acting Oddly
2 months ago I bought a baker's dozen of false neons at a very good price. All looked great, were active, seemed happy and adjusted well. I've got them in my 20 hex with a handful of cherry shrimp, fairly well-planted tank. On Sunday I noticed no activity in the tank, even after feeding. Upon searching, all tetra were hiding beneath a large piece of driftwood, being very nervous. This is a complete change in behavior. If I walked near the tank before Sunday, the little guys went buck wild, all swimming to the front of the tank, anxious that I might feed them.
I checked water parameters, all normal. This is NOT a new tank! I simply upgraded cories out of it and added few plants. I decided a water change was in order. 25% right away, 25% later on in the week. The tetra continue to eat, but this is now the ONLY time they're active.
The tank sits in a far traffic-free corner of my living room. I simply cannot explain this sudden change. Their color is pretty good, though difficult to judge when they're cowering behind driftwood. No visible lesions, blood streaks, clamped fins--just nervousness. Other than water changes and feeding (neither of which bothered them before), the fish are left alone. There are no small children here, tapping the glass . . . so I am utterly stumped on this change. I will note, 2 of the false neons had a run-in with the filter intake and didn't survive, but both were some weaks ago and that problem addressed. Is it possible that losing 2 of their own has brought on this drastic behavioral change? Ideas?