It May Be Too Late...but please help!

Ok, first time grower, had a problem, and didn't want to get too scared too fast, so i gave it some time....but unfortunately, i wonder if i waited too long...lemme fill in the form, and i'll describe the entire situation at the end...

- indoor
- homemade bubble bucket
- b'cuzz grow rokz.
- tap water, adjusted twice daily with ph up and down.
- ph: high 5. using the liquid tester, but definitely stays in the high 5 range.
- age: ~two weeks
- fox farm nutrients
- following their charts, the ppm is checked several times a day, and is kept at about 1500 right now.
- CFLs, the setup is in a garden style tub, we have 7 of the blue spectrum hanging 3-5 inches from the plants.
- temp: not sure, i'm sorry! but it doesn't seem too hot, and our other plants are doing fine in there.
- humidity: once again, not sure.
- light time: 24 hrs.
- fans: one small circular fan which is sealed as an exhaust fan, then one tall oscillating fan to move the air around, and try to keep those stems strong.


ok, so the story. we have two buckets running right now. after two weeks of being in the tubs and these plants looking fantastic, we did a reservoir change on both setups. we had both buckets at almost 1500ppm with a 2:1 of grow big and big bloom, then, like the chart suggested, we did a change and switched to all grow big. i did everything the same for both buckets...dumped them, rinsed them out, filled them, ph'd the water, added nutes and then put the plants back in. this was on friday. over the weekend, the plants in one tub got to looking worse and worse, while the others seem to be just fine. i thought at first that maybe they were a little shocked, but that they would adjust, but as i sit here on monday afternoon, i haven't seen any signs of improvement. so now i'm scared, and i know it might be too late, but i still want to figure out what happened so we don't do it again. also, if it helps at all....the roots looked kinda slimy and brown, even though the nutrient water isn't brown at all.....i took them out and rinsed off the roots and got them back to a color more white, and much less slimy....if it's not too late, please help us save them....they were looking so beautiful before!!!!!

Root rot.
You're going to want to run a solution of hydrogen peroxide through there.

so, 2 tbs/gal of 3%?

just a couple more questions...

how soon should we see positive change?
and
how much has this set my plants back?