I had the same issue ; roots are too bound to upgrade . I had 6 plants in 3 inch pots in a 5 gallon res . I got a 19 gallon tub and cut a hole just below the size of my existing "cover" into the new cover . Now my old cover sits on top of my new 19 gallon res .
I had a humidity issue . I got a 10 dollar electric heater @ Walmart set on a timer with a thermostat . It would heat up the grow room enough to drop humidity from 80 to 50 .
I use current culture for nutes . But would never pay what they want for some plastic . You can get those buckets with the 5 " net pots for 12-16$ a decent pump for 45-50$ and some pvc at your local home improvement store all for under 200. I think you would appreciate it more in the end .
I'm in the middle of building my 2nd DWC . Been experimenting with different pot / resevoir sizes .
Decent size tote / hole saw / tubing / pump / airstone is all you need .
Today is day 5 after my f-up. Tomorrow will be week 3 from seed . After replacing the Resevoir with distill and maintaining 5.5-5.8 ph , water temp @68 ppm at 135 and light @ 16/8 . They seem to be on a better path .
I have a cs feed schedule saved in my favorites but it was the wrong one no wonder why my nutes are all f-up . I added another 1ml of both b+A as instructed for a week 2 . Still only @ 85ppm.If I was to get anywhere near 150-160 I would have to double and add another 1.5ml of both solutions ...