Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
These look like good rocks.
You can test these by putting them into a bucket with water. Test the GH, KH and pH when you start, then daily for a few days. You can run the test out for a week or two, testing every few days.
No change: Rocks will work for soft water, hard water and everything in between.
Small change: You will be able to counter this with weekly water changes. I would not use these for the most particular of soft water fish, but most community fish and hard water fish are fine.
Larger change: Perhaps these rocks are OK for hard water tank, but will create too much change in water parameters for soft water fish.