I don't think your pots are too small. I have had very healthy, fat, out of control 2 foot indicas in 6" net pots on a flood table. Your pots only have holes on the bottom? I have never tried that because Iike my root zone to get lots of air. I have had algae in a flood tray and it didn't seem to hurt anything. I'm hard pressed to find a problem with your setup, grabbing at straws. Pots may not have enough air, LED's suck, EC and PH meters out of whack, I'm stumped.
Yes my pots only have small drain holes in the side of pot at very bottom. I thought would be OK as from what I'd read clay pebbles naturally allow for a lot of oxygen. I don't know.
TBH I wasn't really completely happy with this set up even before problems started this run, even though was quite happy with results from previous runs. I am going to completely overhaul for next run.
I have actually already ordered a new ppm meter as I had a little feeling something was up with current one and I will order new PH meter to be on safe side. Although instinctively I doubt it's a problem with these. I kind of know I've screwed something up somewhere for theses problems to have arised....but as all obvious(that I can think of) parameters are quite well in control I can't work out what.
I took a couple pics with leds off earlier. Although things are still looking pretty bad, I think maybe the very newest growth looks greener and a little better. Perhaps the calmag I added 5 days is having some effect.