hey all, ive not posted much or for a while around here(i'm more of a see if i can find the info myself first) but i am stumped with what sounds like a very similar prob.

i use canna aqua,rhizotonic,cannazyme,pk13/14(in bloom).in a gt424 nft tank with 600hps.growing 4 ppp and 2 pakistani valley.

since the last two grows, since changeing nutes from ionic grow,bloom,boost to canna iv'e had nothing but praise for how stable the ph was. BUT...

around a week ago i was doing my daily checks at lights on and my ph had dropped from around 5.6 to 4.9 i adjusted up to 5.7ish useing gt liquid silicone.next day back down around 4.5 and so it continues.the only probs i can see on my girls are some rusty patches apearing on some lower leaves and the leaf curl as described earlier.another thing i would add is the girls really started feeding faster around the same time.there steady now at 1200ppm,tds from 600 less than a week ago.

from reading around the only thing i can find is possible root rot but my roots are looking better than usual (nice bright white looking healthy).

sorry for the long post but i am STUMPED as i said. so ANY ideas at all would be really appreciated, thanks in advance and good luck yourselves