4 plants, just about ready to be flipped into flowering \t 45 gallon smart pots filled with canna coco\t Using tap water.... So, I think I lockouted my medium. It won't budge from 6.6, and yes I did the slurry test. Mag def is rampage with the 2 Animal Cookies and the 2 Blackberries are now showing signs of some form of def. I tried flushing with Ph'ed water w/o nutes, then with diluted nutes, and still nothing. Getting desperate here, help?
I know this is late, but I was having a problem very similar to that last grow. Were you able to get your pH under control? I found that my tap water was acting as a pH buffer such that after mixing my nutes and pHing the mix, the pH would drift to the high 6s within 24-48 hours every time. Slurry tests proved the medium was also sitting in the high 6s even though I feed at 5.2-5.8 every time and flush every few weeks. As soon as I switched to distilled (RO might make more sense for such large pots in your case) The pH of the medium came down immediately.