Help!! over-watering or Root rot?? or maybe none...?

Thanks!!!ok ill go n buy some H2O2... and im thinking to get out the plants of the rez... then dilute the H2O2 in water.. add to the rez, stir.. then put the plants again in rez..
As i could read, need to put 1 tspoon (5ml) of peroxide per gallon...and wait..

I read that i need to add 5ml each day... is that ok??

Thanks for your help!!