I would not be surprised if you see pH swings up again if your nutes were designed to be used in soil. Often, soil nutes are buffered to come in in the high 6's. Hydro nutes buffer in the high 5's.
Another possible cause of the swings is not changing the res often enough for the weight of the total plant material that lives off it. The greater the plant:water ratio is, the more often you have to change the whole res- DUMP and refill- to prevent nutrient imbalances and the accompanying pH issues and lockouts.
stinkyattic Reviewed by stinkyattic on . nft ph fluctuations. what could be causing this hi everyone i have 25 plants in a diy nft channel (it is just a pice of plastic house guttering) the seeds were started in jiffy pellets and then inserted about half way into a nft plug so that the pellet is above the flowing water and just the roots are hanging in the water flow.. over the last few days the plants as a whole have started to look a bit poor.. and a few of them now look like they are going to die. after spending the last couple of days researching my symptoms i am pretty sure i Rating: 5