pH of rockwool

I'm using a flood & drain hydro system with rockwool cubes as the growing medium. What pH should my nutrient solution be to compensate for the high pH of rockwool?

Thanks!

soak them in water and superthrive overnight ph @ 5.0.

What about the nutrient solution pH during growth? Does the pre-soak take care of the high pH of rockwool permanently, or does pH still need to be lower throughout all phases of growth?

A pre-soak won't take care of the pH problems with rockwool...but a thorough FLUSH of the cubes with plain water PRIOR to soaking them will take you a long way in controlling this rise in pH.

Soaking alone will only put the fine limestone dust (that is used in the manufacturing process) into SOLUTION...and quite a bit of it will simply return to the cube in such a soak.

So flushing them FIRST is the key. If you don't do this..you'll fight that pH rise the entire grow. (because the dust is merely in solution,not rinsed away)

That's my $.02...DIRECT from the Grodan rockwool rep who sells the stuff worldwide.

good luck

bt dt

Thanks for the help! I'll be sure to flush the rockwool before using it.

I'm still a little confused about this rockwool pH stuff. Basically, I'm just wondering if I need to keep the nutrient solution pH lower than the normal 5.8.

In an ebb & flow system using rockwool does the pH of the entire nutrient solution rise because of the rockwool, or is the pH only higher INSIDE the rockwool cubes?

Flush em and the rise will be kept in check.

The pH of the solution should be about the same as the pH in the cube....

I love my salad spinner. After soaking my cubes in 5.0, they get dizzy. All but 1g of water comes out of each cube. They get a 400ppm grow nute @5.5 before plugging in the cuts and until they either go to flower or to become a replacement mum.