Chuck advised me to presoak my rock wool cubes to help balance pH. So, I ran a rather unscientific test. I added a 1.5x1.5 rw cube to about 8 oz of tap water with a 7.7 ph and waited 24 hours. The pH dropped to 6.9.

This probably accounts for my pH ping pong after starting new plants in my nft system. I would test the pH right away, it would be too high so I would lower it. The next morning it would be too low so I would raise it.

Just an observation from a noob that I thought may be interesting.