I have to disagree with all you guys.
It's not root rot or the brown wouldn't wash off like it does in that 3rd pic. And look at the netpot in the third pic where you can see the sludge buildup right at the waterline.
I wouldn't add H[SUB]2[/SUB]O[SUB]2[/SUB] because while I do agree that it's helpful in a disaster, it's a little harmful if there isn't a disaster and I don't think you're in disaster mode.
My guess is that you might have added the nutes in the wrong order and caused some precipitate, although I've never seen that stuff float like yours seems to be doing. Is your water all clouded up or is the gunk just floating on the surface?
Did you mix your nutes up well before adding them to the solution? That Flora Series is seriously thick stuff and it does develop salt precipitates that settle out in the jug. Some folks even get out a drill with a spade bit and stick it down in the nutes to stir the $%&# out of it before mixing - especially if the jugs have been sitting for a long time.
I see you're floating your netpots on insulating foam boards. I suppose there is some chance that the foam boards, or the glue that attaches the aluminum backing, could be reacting with something in the nute mix. Is this the first time you've run this system with the foam boards? If so, try mixing up a gallon of fresh nutes at the same concentration (making sure to add the nutes in the proper order) and then add a couple chunks of that foam board to see what happens.
I love the idea you have about floating the netpots in the foam boards but if your plants get very big, I'm wondering if you'll have trouble with the foam tipping over. Just a thought.
Back to the topic... If you try adding beneficial bacteria, then don't use the H[SUB]2[/SUB]O[SUB]2[/SUB] or the Dutchmaster Zone. Both of those products are excellent at killing bacteria. The tea sounds like a good and cheap fix but it might take a couple weeks to work.
My recommendation is to check the foam in a gallon of newly mixed nutes (as mentioned above) and if that isn't the problem, then dump the res and try a different nute brand like Dutchmaster or Advanced Nutrients that is more of a clean mixing liquid than that Flora Series. Not to knock the Flora Series - it's good stuff.
Hope that helps.