so right now the problem isn't really overwatering, it's just the same symptom of plants not getting oxygen, mostly this is because of overwatering but in your case probably because of bad roots (could be a layer of some residue or rot), so cleaning them in the way suggested above will hopefully solve that and you can water it as you see fit, I think when they are hanging in the air you should be good anyway.
and yeah most people say dilute the h2o2 down to 3% so it won't burn your skin by accident I read this. Or you can just buy the 3% in any pharmacy.