Hi, Denny,

Two thoughts looking at your posts.

You said you add acid to keep your pH around 7.4. Does it rise pretty much on it's own? If so, do you think it has ever slipped up a little too high? If its gotten up around 8 or so, that is probably enough to cause some scaling.

Secondly, I don't understand your FC and CYA results. FC should be in whole numbers and CYA typically is not defineable in less than increments of 10...10, 20, etc.

I know that your question was about scaling but you'll probably need to run your FC up around 6-9ppm with a CYA of 80 for it to be effective.

Dave S.