root rot causing high ph level???

I started a small grow setup about 2 months ago and my plants looks pretty healthy. About 1 week ago, I noticed the roots were turning brown but my plant didn't show any adverse effects. I took pictures of my setup and I think the problem is that my bucket is too small, the roots submerge in the water but I do have an airstone in the water.

The nutrients i'm using is just some stuff i picked up from home depot called Vigoro All Purpose Plant food (10-10-10 mix). I use about 1/4 of the strength recommended on the bottle have a 2 gallon mix in the container. I also bought some algae control yesterday and have added that to the mix because I was getting algae growth in the container. I also keep my pH at around 5.5-5.8 but it keeps rising. When I correctly adjust it, it only takes about 2hrs till it gets to mid 7s. I've also noticed root sediment floating around the mix too.

more pics

It appears from your pics that you just leave a cup submerged in that tub with solution and roots exposed to light, if so then that is your prob. NO LIGHT TO ROOTS OR SOLUTION Put a lid on that tub, put a sheet of the black/white plastic over the lid, cut holes in them both to drop "net pots" in(roots ball up inside of cups and dont escape) and use some nutes designed for hydro and try latewoods formula, maybe a little leaner to start and see how they take it. There is much advice on DWC in hydro section, search recent threads there, get a collective and go from there.........you posted new pics while I was responding...Light reflecting off foil and mylar to under sides of leaves can be troublesome as well

theres a smaller rubbermaid container inside of the larger bucket. I've duct taped the entire smaller container twice to light proof it.