Fish Died From Gill Problem, Pls Help

[dingweding]

currently 3 of my fish died. They become not very active in recently a few days, and died one by one. I check the dead fish, part of their gill turn to white,seems rotten away, the other part still red.

Thus i think it must be gill problem caused by bacteria. so far I tried 1% salt bath for 30 minutes, big water change, also dose 10 ml 3% peroxide in the 20 US gallon tank..

My question is, am I doing the right thing?

there are other fish in the tank, most looks healthy, 2 or 3 not very active, but I check their gill, all red, looks normal, so should I isolate them?

The tank is a heavily planted tank, I obviously do not want to put salt or some other thing in the tank which will kill the plants.. so how should I do ?

Many thanks for your help.

 

[dingweding]

I know definitely gill problem, but I am not sure it is bacteria or parasite.

I did not see any white dot or worm like thing on the gill. Instead the gill has white patch, e.g. the top part of left gill is white while the lower part are red. the right gill, top and bottom look alright, but the middle part are white.

Thus I guess it is caused by bacteria. if Peroxide is alirght, i should I switch off light? how often should I dose? everyday? many thanks