Well from my experience (and it's very little), the waterfarm is just as susceptable to root rot in the rez as any other hydro setup - compounded by the fact that you don't have easy access to view the roots once your scrog screen is down. The best thing you can do, is make sure your rez temps stay below 75 to avoid bacteria growth which encourages algae to grow among other pathogens that menifest themselves with higher water temps such as 'Pythium'. Warm water mean less oxygen, so your roots kind of 'suffogate' and die when it's too warm. I've been told that most roots can handle fairly cold temps, so don't be afraid of 'too cold' of temps in the rez unless you're putting like 30-40 degree water in there...just use common sense.
I'm actually going to have a friend help me this weekend and we're going to left the top bucket out of my VK and lift the screen up at the same time so that it can be raised up enough for us to see the roots. I'll need to raise my light up as far as it goes beforehand obviously...should work okay since the VK canopy has kept fairly low. I still haven't brought in those flagstones to put under the waterfarms in order to keep them cool from below...we may also do that. I've also picked up a great tip from 'Bluejeans', suggesting to put the waterfarm into a shallow pan of sorts, and fill that outside pan with ice-water or cool water to help bring the rez temps down...I may need to try that as well.
Another tip is to keep your air pumps 'outside' of the tent, so that the air they pump into the rez is cooler than the warm air inside the grow space...one of mine is outside of the tent - but the AoS pump is inside..may need to move it out of there!
I asked my hydro shop guy about using too much H2O2 (hydrogen peroxide), and he said unless I use WAY too much (glugs of it at a time), it will be fine and actually beneficial for the plant, even if there's to temp or root rot/algae issues... especially when using the over-the-counter 3% stuff...which is what I'm using - just from the drug store. Many hydro growers use it regularly, even if they aren't having these issues. THe hydro shop sells the high-concertrated H2O2, and it's pricey - but for just a few waterfarms, the 3% stuff is fine. I use about 1.5 tsp per gallon in my add-back pails, and about 2.5 tsp per gallon in my full rez change-outs. Since using it, I've noticed my algae went away that was building up on the AoS... H2O2 will not effect your bud taste - it's just like adding liquid oxygen to your water. H2O2 is missing a molecule, and when it breaks-down in your water, it releases pure oxygen, which the roots absorb... no effect to your plant smell or taste.
Hope that helps!!
If anyone out there disagrees or finds this info inaccurate, please jump in here!!