One reason for low CH may be all the rain we are getting here. It's rained most days, for two weeks now. Some days multiple inches. A couple of weeks ago we were down 6" for the year but a couple of days ago made that up and now have met July average already.
I've been battling low CH since I converted in summer 09. (I didn't pay much attention to numbers other than FC before finding TFP

hence lots of calcium scaling for 23 years.

) Fall and winter were one of the cloudiest, rainiest fall/winters on record. Between that and backwashing every 7-10 days before I decided to just open filter and clean AND forgetting hose and overfilling a few times seems like I'm constantly adding calcium. Mines around 300 right now, due to just having added calcium last week. (It's actually less as I let out 3" water Friday.) I usually don't bother letting water out until it gets up over the top of skimmer opening because the sun and wind will evaporate it pretty fast, as much as an inch a day (and multiple big dogs' splash/carry out).
BTW... The calcium increaser at Walmart is only $5-6 for four pounds.
gg=alice