Auto fastbudz

All was going great but now the soil buffer has gone so starting to ph water(tap water 7.8)PHing to 6.3.flowering has pretty much stopped or slowed right down I'm at a loss. Day temp is 23 night temp 20,im adding 0.2 calmag and 0.3 biogrow(I'm using biobizz lightmix and I've allways had this problem and getting abit bored of it now what ever I do i can't seem to fix it. Plants look healthy, on one of them I had N tox, flushed with PH water but still seems to make no difference.