Chabnoc, I also have to adjust pH down frequently. I do all the prep that Zandor and LOC NAR both describe for the rockwool cubes and a bit more; I flush my cubes under running tapwater before doing the pH 5.0 24 hour pre-soak. Along with my controlled clonebox conditions, this gives me utterly reliable strikes in 6-7 days.

However, I use loose rockwool floc in pots in my flood trays. It's simply not practical to soak and drain 23 8" dia x 8" tall pots of floc. I'm told (but haven't confirmed) that rockwool has some limestone residue left from manufacturing and this is what causes pH to jump up.

For me, it's no more trouble than adding about 5-10ml of pHDown sauce to my 125L tanks every couple of days to bring the pH down to about 5.3-5.8.

Please have a look at the link to 'A batch of clones in rockwool' in my sig. May or may not be anything useful for you in there.
Al B. Fuct Reviewed by Al B. Fuct 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