Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
There used to be one that definitely did raise pH, it was designed to do that for hard water tanks.
Then there was some problem about the 'regular' EC also raising pH, but the idea was they had corrected that problem.
That was quite a few years ago.
Is the problem coming back?
I think I would rinse it really well, either in a bucket or by doing several water changes with deep vacuuming, then refill and see if the problem persists. It should not. The basic material EC is made of is inert. It is the additives that might be the problem. They are in liquid form, so once they are rinsed away that should be the end of it.