Fin rot??

[Danio35]

I bought 3 Red-Eyed Tetras one week ago and I'm concerned they may have fin rot. It is worse with the smallest fish. His front right-sided fin look almost like someone chopped indiscriminately at it with small scissors. He swims almost vertically and to one side. His top fin is also that way as well. One of the other Tetras top fin is like this, too. I just noticed today that my Pearl Danio's top fin is like this. They all swim around fine and are eating and appear to be in no distress.

He was acclimated slowly to the tank using the drip-method. He is in a 10-gallon tank with the following:
UGF and Aqua Clear 10/20.
Water parameters from yesterday pre-20%-water change:
PH=8.0
Nitrites=0.5
Nitrates=20
NH3/NH4=0.25
GH=300
KH=180
Temp=74

His tankmates include:
5 Danios
3 Hatchetfish (I bought them before I knew their requirements. Bad idea on my part, but they were so cute!)
2 other Red-Eyed Tetras (already mentioned)

I know my tank is overcrowded. My 55-gallon is currently in the process of cycling and doing well. I bought the Tetras and Hatchetfish on a spur of the moment weakness, before I was ready. I realize now, on hindsight, that I should have just been patient, paid attention to the health of the fish I bought and just waited until the 55-gallon was ready. Now I'm thinking I need to put some cash into a quarantine tank or just keep the 10-gal as the QT.

So many choices, so many fish, so much equipment, I love it!

[TankGirl]

I don't know if you have had any resolution to this problem, but I see that the 10gal is cycling as well, and this is no doubt contributing to the stress of the fish. You can treat fin rot quite effectively with Melafix, and it will not hamper your cycle in any way. The addition of fish during a cycle makes it trickier but keep up with your water changes, and if you can get some Bio-Spira that will help immensely.