This is the second tank I have used Caribsea Live sand and have had this issue. When tank was initially set up, my ALK and CA requirements were triple what I normally would need in a 100 gallon tank. I was dosing upwards of 140ml daily just to keep numbers even close to 8 ALK and 440 Ca, with very little coral. At the same time, I could not keep phosphates in the tank....I would triple dose daily and they would be gone the next day. This went on for almost 6 months. I would stir the sand almost daily, except for the areas that were directly under the live rock. Fast forward 9 months later, I decided to remove my substrate. Within days, my ALK and Ca requirements dropped down to 60ml daily and I no longer have to dose PO4. Also, directly under each piece of live rock, the sand turned to concrete, fused to the rock. I liked the look so I left that in the tank but removed the rest. What process causes the sand to absorb so much ALK and Ca to cause it to harden and fuse together? I see threads all the time about new tanks that can't keep levels up....I wonder how many of these are associated with the sand bed?