ph of less than neutral will start to erode(sp) their shells. The acidity in the water is the cause of this. You also need to have a decent kh, my guess would be 6+. You could add kh to your tank by adding crushed coral to your filter. This will rise your kh and your ph and will make it harder for CO2 to dissolve, but your CO2 should still be fine. I currently have red ramshorns, mystery snails, and a few smal spixi's. I havnt noticed any erosian on their shells though I have had them for about 2 weeks. My ph is in the 6.8 range and my kh is 7. I do not belive that they will be dying from my ph and I judge that they are more than happy with my kh. I also wouldnt reccomend adding kh to your tank if you currently have soft water fish and/or plants. I hope this may clear a little up. I am no pro on this so if anyone else wants to correct me or add please do so, you will be helping me learn as well.
I raise my sword in the air in the battle against clado. I have been beaten in this battle but the war is not over. As my wounds heal I amass another army, an army with many legs, an army of Amano's......
I thrust my tridant into the mass of medusa like staghorn. I am wounded but I refuse to take a knee.