I have had to do the same recently to make sure I wasn't locked. I use a float valve in my control units with RO top off, and by shutting it off for a couple of days, it gives you a true indication of what they are doing, and what they want...I have been working on dialing in the correct EC for my diy uc's. I used to just use the float valve maintain the water level with just ro water. Doing it this way I really had no Idea what the plants were asking for. This time, every few days I will turn off the top off res and let the plants eat what they want and let the water level just drop a few inches. Wouldnt you know it it works exactly as its supposed to. If the nutes are too high the ph will drop and if thier two low the ph rises and the ppm's drop. I have been giving them exactly what they want this whole run just a little on the light side. I havent had to even touch my bottle of ph down at all. Maybe this is common knowledge but I just figured it out myself. Before I was way over feeding them getting burnt tips and discolored fan leaves. This time the plants look super happy and healthy..