Root rot? ways to fix?

[greenhydro]

I have two bubble buckets and just got everything right or so I though. Now it seems the roots are truning brown and falling off in the tank, they seem kind of mushy. Thats why I'm assuming it root rot. My question is how do i fix it? Ill list what ive done so far to let you have an idea.

-4 gals water in black 5 gallon bucket
-5in bubble disks
-pH water down to 5.8 drift a few days then lower again.
-Use SH nutrients (grow, micro, bloom)
-Water temps fluctuate low 62 high 70

any ideas what i can do to fix this?

you can kind of see the browning on the roots

this is a brown slimy root that was floating around

the leaves just started to wash out like this.

 

[greenhydro]

I have been reading that H2O2 will help this but why do i keep getting it in the first place? the temps stay under 70deg 90% of the time.