To keep your roots white and crisp, you need to keep water temp under 70* and use h2o2 or bennies (beneficial microbes). The h2o2 sterilizes like bleach by killing pathogens (and other microbial life... for this reason you can't use h2o2 with bennies). The bennies keep pathogens under control by out-competing them (and they provide other benefits as well).
Both work for prevention, but h2o2 will most likely fail against high temps (mid 70s) or already established root rot. Some people like Heisenberg claim h2o2 even slows down root growth in clones. For this reason, I prefer bennies. Some simple/cheap options are Botanicare Aquashield or Pond-Zyme (from PetCo or Petsmart). With one of those options, the cost and effort of using bennies vs h2o2 is about the same either way. There is also Heisenberg Tea if you want to get fancy. If you go with sterilizers... instead of h2o2, a lot of people use Zone by Dutch Master. People also use bleach or Pool Shock chlorine.
The nutes you are using contain organics which could trigger slime blooms in your res unless you use bennies. Also, you need bennies to convert the organic compounds into usable nutes. If you were to use h2o2, the microbial life would be dead, and nothing would be converting the organic part of your nutes for the plant. I would go with Dyna-Gro until you get the hang of things. It's cheap, ph stable, non-organic, complete with all micro nutes, time-tested and proven in the agricultural industry, and simple 1-part Grow bottle for veg, Bloom for flower. Most people add Pro-Tekt during veg (silica for hardening branches, heat and drought resistance, etc) and Cal/Mag.
General Hydroponics Flora 3-part series is another popular choice for DWC with many of the same postives as Dyna-Gro. A lot of people use the Lucas Formula which is a cheap, simple, and effective feeding schedule using the Flora series. Stay away from FloraNova, it contains organic material which could fuck with your roots until you get things under control.
For your temps, assuming you are using 5 gallon buckets... wrap them in 3 layers of reflectix from home depot or lowes. They will be insulated AND 100% light proof which is crucial in DWC. I have tried coleman/rubbermaid coolers and buckets wrapped in reflectix, and the reflectix works better for me. You should be able to use 1L bottle of ice every 24 hours and stay well under 70* assuming 'reasonable' ambient temps.
If you want to learn more about the roots and DWC... check out the sticky thread breeding beneficial microbes and just skim through it and only read Heisenberg's posts (because it is sooo long)... the thread is a fuckin gold mine.
