I could be wrong, but I believe the problem is the soft water, because of the salt in it.

Try a res change with store bought water and see if you get the same PH fluctuations.
Perp Reviewed by Perp on . Need a little advice. I have just started my first hydroponic grow, think it going ok so far, my plants have been in the big blocks for about 6 week's (see photo) and now using half strength canna aqua vega 1&2 , just need a bit of advice on when to start 12/12 with my hps. Has anyone had trouble when you add the aqua vega messing with the ph, i have soft water where i live and only need to bring the ph down a fraction, when i add the aqua vega the ph is too low and cant get it up without losing alot of water and Rating: 5