hey bro, your shit looks real good. ive got a DWC system in some five gallon buckets and its kind of a pain in the ass already to change the water every week, and ive only got one plant per bucket. im curious, what is your method when you put new water in. is it a two person job? right now i just put an empty bucket next to the plant and lift it and the roots in the empty one and rinse out the other bucket.
My plants sit in 2 gallon tanks and drink 3 gallons per week. I don't have to do any water changes.
You have bigger tanks which should produce bigger plants and if your environmental conditions are optimal your plants should drink the same ratio as mine. As long as pH and PPMs stay consistent through the drinking process even with top offs you know the plants are eating and drinking in a balanced fashion. Spikes or gradual climbs in PPMs mean the plant is leaving certain nutrients behind which eventually lead to climbs in PPMs as you top off your tanks. To solve this, allow your pH to drift up and down between 5.5 and 6.5. This allows the plant to take up a wider spectrum of nutes.
Ask anyone who maintains an aquarium if they do a complete water change every week! I have a 15 gallon fresh water tank...I don't think so.
A properly maintained water system will eventually establish a colony of beneficial bacteria and microbes. These microbes (although not effective against bugs) will eat all of the rotting material in your water including all the bits of roots which fall off along the way.
Observe your water throughout. It should be a bit cloudy and only bits of fresh root material floating around. That's OK as long as you don't see any dead brown bits. It should smell fresh, almost no smell. Your roots should smell like fresh lettuce or alfalfa sprouts.
The question you should ask, if it's been 10 days since your last water change of 5.8 pH and PPM of 900 and today your water reads 5.9 pH and PPM of 910 with clear, fresh smelling water, what do you want to do?
I know what I'd be doing!