fin rot/loss on one of my cory panda

[Delphe]

Hello,

As my entire house is on survival mode for a couple month a take 5 minutes to ask a few questions.
Well, first I have to confess I didn't vacuum the substrate or clean the class and ornaments since the 3rd of October (used to do every saturday morning), What I did is change 1 gallons of water every evening and every morning (I have a 29 gallons tank) and was able to clean the filter last Monday) if I can't give it an hour, I can give it 5 minutes morning and evening.
I probably won't have time to clean the tank before the first week-end of November.
So last Wednesday I saw one of my cory panda having fin loss, tail half way and a start on the dorsal one, took the time to do the parameter and ammonia & nitrites are 0 nitrates around 10ppm which is higher than what I ever had. Nevertheless, at 11.30 pm I set up the hospital tank and started treating that little guy for bacterial infection as I don't have time for wait and see.
- How long does it take for the fin to grow back after treatment?
- Harvest is a bad spell but comes every year, any thought on how I could preprepare the tank for it next time?
- Anything I should do to watch the tank and the others pandas?

Any advise?

thanks,
Delphe

[Delphe]

I read that fin rot or loss could be sign of poor water quality, aggression, stress, and variations...
I don't understand what I do wrong for that fish to get that:
I only have the pandas in the tank along with 3 nerite snails right now and the only variation there is, is disturbance from that one gallon water change twice a day (which I did to keep the water quality in check), would it be enough to stress them ?, should I stop? Is there any better way to go about it?
How long should I keep my little guy in the hospital tank?

Thanks,