Ya loc nar has it right. You must pre-soak rockwool at a Ph of 5.2 to 5.5 for 24 hours before you first use it or you will have the problems you are now having.

In hydroponics you do need to adjust the Ph several times a day too that is normal.
Zandor Reviewed by Zandor on . First time with rock wool. This is my first time useing rock wool. Seems to be working pretty good so far, but the PH is going up each day. I am useing R/O water, and I ph it to about 5.5, by the next day it is up to over 7.0. It is only been 3 days now. Is this normal, and if so, we it get better with time? I am useing the same nuts as I used the last time, and my PH was real stable. Thanks for any help. Chab. Rating: 5