PH is 4.9 - What could be causing this?

[Atl300zx]

The snails that died were about 25% the size of the largest fish. However, i just found empty shells, that is how i determined they died.

 

[7Enigma]

The snails that died were about 25% the size of the largest fish. However, i just found empty shells, that is how i determined they died.

Empty shells sounds like they were eaten to me. When they die naturally they stay in the shell and get a fungus/bacterial film over the opening to the shell and start to smell really bad. Trust me, I have been trying to get a snail breeder tank going at work and have lost several groups of snails to most likely a copper/heavy metal issue in our tap water (gee glad I've been drinking it too!). When those suckers went, I came in after the weekend and had to QUICKLY get rid of them before coworkers gave me problems.

 

[Atl300zx]

So an angel fish (~6 inches across) or bala shark (~5 inches long) can eat an apple snail the size of walnut? that blows my mind.

 

[gu2high]

I personally ate hundreds of snails, so I think the fish you listed can eat the snail too. Even my 2 inches dwarf gourami attacks apple snail occasionally.

 

[Purrbox]

Basically all GH is important for is to make sure you are not deficient in the macro nutrients Ca and Mg.

Does this explain why snails never did well in this tank (never last over 1 month)? I have an apple snail in my 10 Gallon low tech, low light tank and it is doing well (4-5 months in that tank)

If you have a low GH then it's likely that the snail won't do as well, but it's not necessarily the cause of their death. The way to tell, is to look at the shell and see whether or not it appears eroded. When there isn't enough Ca available the shells will get holes, and if they go all the way through will cause the death of the snail.

I've got a 1" Dwarf Puffer that eats snails about half it's size.