I've read this thread from the beginning and can see no reason why corals and snails die on you.
However, I do have a few suggestions that might be of use generally speaking. If this was my 110g, I would:
- reaquascape to get rid of the "wall of rock". This would provide better flow throughout the whole tank.
- make sure you get good water surface movement to maximize air exchange between the tank and the air in the tankroom.
- make sure the room your tank is in gets fresh air. This will eliminate the possibility of high CO2 levels in your tank room and thus in your tank. High CO2 levels will often show up as low pH in the tank. You can test for CO2 levels in your tank room by taking a sample of tank water and aerate for 20 minutes with an air pump. Record pH before aeration and after. Then take another sample of tank water and aerate it outside for 20 minutes, recording before and after aeration pH. If there is a big difference between inside aeration pH and outside aeration pH, you don't have enough fresh air getting into your tankroom.
- add non-invasive macroalgae in either the sump or display tank to utilize excess nitrate and phosphate. The reason there is no nitrate/phosphate in your system is that the hair algae is using it up. If you had an excess of phosphate in your system, it would show up as cyanobacteria.
- reduce calcium to 400 ppm. Alk is fine at 9/10 dKH. Temp looks good, too. Also test for and adjust Mg to about 1325 ppm, though even if it is a bit low or high, it should not be the culprit in dead snails or corals.
BTW, I have had a number of low or high levels of the above mentioned Ca, Mg, alk, pH and have not had a problem with dying livestock. However, when chemistry and pH/CO2 levels finely tuned, I get better coral growth, better polyp extension and better coralline growth.
Do the pH/CO2 levels test and let us know what you discover on that front. It could be one of the bigger factors with your dead snails and corals.
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