Hmmm. I am tackling Phrags for the first time as well, was using totally pure water and have special slotted pots to help air get in, fans for circulation, special custom mixed Phrag media etc. I got them last April then we had a wretched HOT summer with temps in the upper 90’s. Suddenly all but 1 of the 8 Phrags have shown extreme distress. Leaves dying back and my Fritz Schomberg currently has roots but NO growth on top! It has totally died back! I was told by expert growers that the extreme heat was to blame. The distress is pretty much over, and I reduced the fertiliser, I continue the weekly flushing with pure water, but see no “forward movement” no new growth and no change in the current growth! Sigh! Basically I am told I am doing everything right and things should turn around! I just am impatient I guess!