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Beware of cheap imitations they cost a lot more in the long run.  Grodan is the undisputed leader of the rockwool market and is used by both commercial and hobby growers through out the world.

We stock a full range of high quality rockwool ranging from small starter cubes to large slabs.

It is a common belief that Rockwool has an unstable pH and that you have to continuously adjust the pH.  This is not true.  When Grodan rockwool is new it contains some residual lime from production.  Everybody should soak the rockwool in no lower than pH 5 water the day before use.  This is done to dissolve the lime.  The lime will make the pH value raise a full point.

Immediately before use; you flush the rockwool with your nutrient solution.  When you flush, you also flush out the dissolved lime.