I completed the test using strictly pH down and plain water, and apparently that works. I am not sure at this point how much pH down is needed to get them clean, and how economical it would be to do in large amounts. I used
Earth Juice Dry pH down at about 1/4 to 1/2 teaspoon, and about 4 oz water (or half a coffee cup full). That is about half the amount I need to adjust 8 gallons of
nutrient solution depending on how far off it is. I simply wanted to see if it would work so I intentional made it extremely strong. But as you can see by the pictures it did. I let it soak for over 48 hours to be sure also.
After using the bleach water to sanitize the
grow rocks, and then soaking in boiling water a couple of times the ones from the vinegar tests, all but maybe a faint trace of vinegar is left that I can smell. I will soak them in boiling water again once or twice just to be sure. I am at this point cleaning all the grow rocks in about 1/4 vinegar and 3/4 water solution, and will let them soak for a couple of days also. Then fallow the same sanitizing and rinsing/soaking procedure to get them ready to reuse.