I have been having this problem for some a good month with my 2 nycd x g13 from Soma in a 31 gallon rubbermaid, DWC gh nutes, lucas formula, 400w hps, in a wooden armoire, temps stay between 70-85 and rh is 40-60 %.
The ph just keeps dropping, I flushed with plain tap water (~130 ppm) for a good 8-10 days and the ph would just keep dropping to like 3.8-4.3. ppm would stay about the same maybe drop a little. But it didnt go up, ph never goes up in my setup. Maybe I am undernuting? I have kept the ppm at around 700-800 on a .7 conversion. I have an expensive hanna meter thats calibrated so I know my readings are pretty accurate.
I read somewhere that maybe its because I don't have enough nutes that the ph is so unstable? What fools me is that the tips of the leaves are burnt, much like nute burn, but when i flush and flush the plant doesn't dump anything major back into the res.
Sorry if this is posted in the wrong section, just don't know what to do, so frustrating. Also, both plants are almost 4 feet tall, vegged for ~30 days under a 125 500k cfl, in about week 8 of flower. Some of the leaves are starting to turn pale yellow like they are lacking nitrogen (from the flush i guess) but im scared to add nutes as they already show symtoms of nute burn (burnt tips, edges, stunted growth) maybe this is a deficiency?
any help would be appreciated, sorry for the lengthy post, and i did search a good deal.