Thanks for the reply, Krip! Also, another question. How often do YOU change the rez? Do you add in more nutes and Ph it or dump the entire rez and add in fresh batch?
I do a complete res change once per week. When I do, I completely disassemble the waterfarms, soak the pieces in a bleach solution, rinse thoroughly and re-assemble.
During the week, I'll top off the res with plain, NON-PH'd water, then adjust the PH of the res as needed.
The waterfarms hold 2 gallons of nutes in the bottom res and the "rule of thumb" is that you do a complete res change, then top off with plain water daily, as needed, until you've replaced a total of two gallons of H2O (basically, you've added as much as the res holds), then you should do a complete res change again.
I find that, until late into flower, they're typically drinking less than 1/2 gallon per day, so weekly changes tend to work fine. Occassionally, if they've been drinking heavily, I'll give them a "booster" dose of nutes during the week.
The best way to do this really, is by measuring PPM's. If PPM's are going down, it means she's taking in more nutes than water and needs more nutes. If PPM's are going up, she's taking in more water than nutes and just needs a water top-off.