Hydro dripper system

I have 9 clones in a hydro dripper system it,s my 1st hydro grow always been in a soil bed till now they are doing ok up 2 now 2 have died no idea why they look like they thristie plants but they have been feed as much as the other 8,i was just wondering how tall should i let em grow b4 i flower im hopeing 4 at least an oz off each 1 at the minumum any 1 who is a hydro grower let me now i using the best of the best nutes (canna aqua ) a an b an rhizotonic 4 rooting this is veg stage for flowerin im useing the boost acclerator an canna flores a an b a 400 watt hps an a warter heater at 17-18 i have a grow tent 2 4 inch rvk out take fans the temp in the tent is between 75-80

water temps need to be below 75F, this is root rot territory, also whats your medium? rockwool? or a cube in clay pellets? maybe your dripper was getting the rockwool too saturated?

There in 3 inch rockwool in clay balls the dripper goes on 4 times a day for 15 mins each time .the light is 15 inch off the top of the plants i started with the light 2ft above the plants when they 1st went in, they will be 2 week into veg on monday 8th of june there growing pritty fast an bushy,im going for a minum of 1 oz off each plant easy done an oz off each.how tall should i let em grow,in soil i let em grow to 2ft then flower an i get around 2 oz may be just over but never ever under i use hesi when i grow in soil but now im using canna aqua for hydro growing.it,s so much faster than soil.my p.h is between 5.5-6.2 never let it go over 6.2 an never under 5.5 the nutes i put 10ml in 10 litres of aqua veg an the rooting stuff should be 40ml to 10litres but i only put 20ml in