I started a second QT tank, 29 gallons, and have started dosing copper but not reaching therapeutic levels. Currently have a flame angel, goby, leopard wrasse and two flasher wrasses in the tank. Given the goby and wrasses, I decided to put a take out container of sand in the tank. The sand is quikrete from Lowes, which I thought was supposed to not absorb copper. So far I have dosed 25ml's of CopperSafe and still not above 2 via hanna checker. Is this expected with the sand?