I would definately rule out your cal and alk levels as being a problem. Untill I had calcium reactor, I would have to fight to get my calcium even as high as 320. alk would be 6-7dkh, sps were always healthy and grew anyways.

I would maybe question that there might be something in the sandbed. It could be a lot of things. Phosphates, metals, who knows. I'd start doing some more unusual tests.

I had endless trouble keeping some acros and montis in the past. I lost a lot of them. I never thought that it could have been my PH until I bought myself a Pinpoint PH monitor. Now, I could see that my PH was about 8.1 during the day but 7.4 in the morning before lights on. Since making myself a Calcium dispensor for my Osmolater recently, my PH in the morning is 7.7 and during the day is 8.2. I think I was losing acros because of PH and not from high nitrates that I thought in the past. My acros and montis are doing much better now.

J, just a small Colt and Frogspawn, the rest are SPS.