I cant believe you didnt use h2o2.
h2o2 is god for hydro, it will:
Prevent Root rot
kill bacterias
sterilize the res
increase oxygen levels
increase root uptake capacities
increase growth/yield
probably make you refill your res more often
Ive been using h2o2 on a small hydro grow, and its amazing the bushes a 4' x 40 watt fluoro setup can make!
I urge you to add one ml/ per gal/per day of h2o2 into your res and be amazed to see those roots whiten up like a smoker after a whitening trip to the dentist.
YES PER DAY, h2o2 dissipates quickly, try not to leave the bottle open either, dont get any on your skin or clothes, it will act like bleach for your clothes, and make your skin turn white and burn for while, depending on degree of exposure. Dont get any of the concentrate on the roots themselves, and dont apply to foliage, doing any of this will result in the localized death of the spot where it made contact.
Just get a little dropper and drain it into the water, it will circulate.
I also recommend another air stone/pump as with the h2o2 your uptakes increase and your plants will show you how much they love the extra air.
Since your res is overgrown with roots, I would suggest diluting the h2o2 into a couple liters of water, as you pour the solution in, the roots may react still to the h2o2. but this is for the better as it would hardly lose a beat, and you can now see the bottom of your res!