Quote Originally Posted by pentachris View Post
I'm guessing that's the blow-through
Don't jump to that conclusion. Not all of the calcium in cal hypo is insolubles that can be filtered. To actually test your filter, get couple of pounds of DE powder, and put THAT in your skimmer (it won't react with cal hypo). If the DE blows through, it's a filter problem. Otherwise not.

Your CH level is so high, the soluble portion of cal hypo can still trigger some precipitation, visible as cloudiness.

ALSO, a sand filter will not grab the cal hypo insolubles well just after it's backwashed. When using cal hypo this way, you want to back wash as much as you have to -- 7 - 10 psi pressure rise, but no more than that.