I have a 29 gallon coral life biocube that's about 2 years old. I have tons of coralline algae and multiple pieces of LPS a BTA softies etc. 2 small clowns and a pistol shrimp with ywg and a mandarin. My problem is that after a water change my all is at a 8. After 3 days or so it drops to a 4 or 5. I used two different test kits one being API reef master and nyos. Same reading. PH is fine but cal is low and I have a MG test kit coming in his week. My question is why such a large swing? I understand that coral and coralline consume carbonate hardness for their skeletons. But a buddy of mine has the same setup as me with far more coral and has no issues. I use coral pro Red Sea sea salt.
