first of all how big is your res and what size table are you useing and are you useing rockwool at all. are they in veg or flower and how many times a day do yu feed and for what duration if in veg it should be 4 times a day for 20 minutes or so flower 3 tmes a day 20 minutes or so. wild fluctuations in ph could be due to useing rockwool with a small res the minimum size res i would ever use is 75 to 90 gallons much more stable and easier to control ph. clay balls will have little or no effect on you ph unless they have salt build up on them its agood idea to flush the res every 7 to 10 days dont go past two weeks.