I had Draco for about 8 months. He was perfectly healthy all the time, then about a month ago, following a water change he got sick and died. I have two other bettas in the exact same size and style of tanks and had cleaned both of their tanks on the same day and they're both fine still. Anyways I bought a new betta after cleaning Draco's tank and put him in there with new leaves and a new cave. Anyways this new betta was also pretty healthy. He was strange and would bury himself beneath his rocks, but once again following a tank cleaning he got extreme fin rot. I tried to get him better using aquarium salt and melafix and he seemed better, but tonight he died as well. My other 2 bettas are doing perfectly fine so I'm kind of confused about why these two bettas died. It can't be the water since the other two are fine, but they both died after I cleaned the tank. I'm wondering if the tank may be carrying something and if so how could I fix it? I don't want to put other bettas into the tank for them to die as well and I'm really upset over these bettas deaths.
I'm not really a betta pro, but I've had one betta perfectly healthy for 2 years and my other has a couple of problems from before I got him and I've kept him happy and healthy as he can be for a year. They're both thriving and both of these guys were fine until I cleaned their tanks. I figured I should ask here since everyone probably knows a bit more about raising them than I do.