If you can find Dowflake or Pelaflake, that is your cheapest bet for Ca. Many have used Prestone driveway heat and had great results. I was dosing the liquid, but had to dose so much that it got easier for me to start dosing three heaping tablespoons of Dowflake every other day (dry, mixed with RO at the time of dosing) and three heaping tablespoons of baking soda every three days or so (uncooked-dry, but mixed in RO just prior to dosing). This was in a well stocked SPS tank (125), though. I think that should have been too much, but the test kits were tellinh me I needed it. My magnesium was likely off (it seems to help the balance stay stable). One thing you don't want to do is drastically overdose and bring the values up quickly, so start slowly and bring it up over a couple of days. Then monitor frequently until you get the right amount and frequency figured out.