I had bought a VT last weekend.
When I got him he was active, but he was not eating.
I put him in my 10 Gallon, heated (temps around 80 degrees), filtered, aerator.
At first he was OK, and would chase the Glowlights around a little.
Eventually they were leaving him alone because of it, and he picked to be mainly at one side of the tank, but would occasionally venture around.
However, the past two days he has been laying on his side at the bottom every so often. I was assuming he had light sensitivity issues as he would rest as if to avoid the LED lighting on the tank. I was indeed concerned for worse as well, but I just have not been able to get him out of the tank since he hangs out near the bottom when he is active and avoids me even when I'm just observing him, sneaking behind objects all shy.
Yesterday in the morning I fed my others, and took note on where he was and how he was doing before I left to go through my day routine.
I get back 10-11 hours later, initially thought nothing of the tank, and proceeded to tend to the others.
I finally started questioning the 10 Gallon tanks water clarity.
I look into the tank.
Oh, so he died? (The VT is stuck on the filter intake looking dead)
I get my net, fish him off it, and put him in his original cup.
For some strange reason my inner voice/impulses tell me to put water in the cup as I put him from the net into the cup.
I fill it.
I put the cup on my desk.
He started off rather bad. He was face up in the water, tail on the bottom. I decided to remove as much of the tank water from his cup as possible and give him fresh spring water I got the day prior (so it is room temp by this point).
I left him over night, the cup half filled so it is easier for him to get the the water surface and not struggle as much (because he was straining to the surface).
I've been observing, and it is very borderline what will happen to him.
I'm having trouble telling, but he could have dropsy, as I'm not sure if he is slightly pine coning or not due to his white bodied coloration. His under side where his ventral fins are is whiter than the rest of his body, not grey, which also confuses me in diagnosis.
He has leveled out his balance, but every so often I catch him not moving any of his fins, meaning he stops moving his pectorals. He is being VERY idle most of the time. I feel he is dragging his back fins entirely as if he does not have any energy to really use the caudal fin as a betta normally would. He sometimes moves, but it is short bursts, followed by more idle.
I'm not sure what more I can do for him than give him time in the cup. I also decided to put some blackwater extract in as I hear it is good for these guys (I try to in all my tanks, but in filtered tanks it doesn't work out as the filter just absorbs it within 4 hours).
Picture is what he looked like on Thursday/Friday so you understand why the color is confusing me. I typically don't go for VTs unless they have a coloration that is unique like this guy.