I too think it was pH. I calibrate weekly now or if I get a whacky number.

Also, I think I had pH issues with the hydrotron pellets (or whatever those little brown balls are). Learning is fun!

I did not realize the formula had been revised. That's actually great news--I had not switched yet and really didn't want to! I'll have to research that more.

Thanks for all the help everyone.

Buzz