BettaMomma said:
...After I take the fish out I run scalding hot water over the gravel and swoosh it around, then dump it out. I do that 3-4 times before I'm done... then I wipe down the edges of the aquarium and then fill it back up.
Hi BettaMomma
Why are you doing that? There is no way that the tanks will be able to cycle unless you give the beneficial bacteria a place to live undisturbed. Your small tanks are big enough to cycle just by doing good water changes alone and letting nature take its course. Vacuum the gravel, but beside that, leave it alone.
Finrot is caused by bacterial infection. Perhaps your fish doesn't have finrot. If you are not keeping the ammonia levels down at all times, the ammonia alone is enough to burn them and damage their fins. AND, the drastic chemical change in the water from before to after water changes is apt to be a worse stress for the fish than netting them ever could be. That will lead to bacterial infection.
If you keep the chemical levels low and steady (either through frequent small water changes alone, or cycling and less frequent water changes) and cure the bacterial infection (if there is one) your fish will get healthy and stay that way.