Attachment 281098

This is a Myron L T6 pH/TDS combo meter.
No probe replacement needed, just keep it moist and recalibrate every 3 months.
I have owned these meters for over 8 yrs and no fails.
downside... they cost around $400. In the long run that saves $ though because you dont have to buy probes.
These are extremely accurate meters. put two side-by-side and test water from the same source and you will get the exact same reading. try that with digital meters.

Good call with the over watering... all i could see was the hydroton so I didnt think that was possible. But rockwool is, like you said, a super sponge.

Good luck with your project.

By the way, if you really like top feed set-ups, try using 1/4 minus pea gravel. I know it sounds strange, but when I tried it I have never seen roots more bearl in my life. plus its super cheap and so heavy there is no way a plant will tip over.