Hello;
I find it useful to test as Snowboarda42 does. Everyday at the same time while determining dosage, as CA and Alk can and does come from other sources in the tank. So, you only use 50-ppm a week --- that is a very small usage as I use 3-dkh and 60-ppm a day --- not that the coral, coralline, or heater uses it all --- it is just what is takes.
My pump impellers are all clean, I have no Calcium Carbonate or caking of my substrate --- just a little deposit on my heater. Goes somewhere.
AP test kits are cheap --- the KH test kit reads dkh directly and is accurate --- the CA test kit is within 10-ppm according to my shaky, poor eyesight, comparison with my old Seachem test kit.
I would use these --- I do, I test for Calcium and Magnesium once a week and ALK a little more often --- you only need to be close or in the middle -- 7-11 dkh and 360-450 ppm CA. Just stay in the middle I always say.
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"It has to be right, I read it somewhere!"
"OFM"
Enjoy!
OFM