It doesn't seem like there is a lot of information on this topic (or I just suck at searching), but I'm wondering at the main differences between using CaCO3 (crushed oyster shells) and CaSO4 (gypsum) to supply calcium to casings. So far this is what I have come across:

"Calcium carbonate (CaCO3) is pure limestone. Gypsum is impure calcium sulphate (CaSO4). Apparently both will work, but the CaCO3 will work better over the long term because carbonates are generally: less soluble than sulphates (more of it will remain as a solid until an acid comes along), less reactive (less likely to be transformed into some other molecule), and is less acidic (the sulphate ion is one of the species generated when sulphuric acid is mixed with water as part of the H2SO4 <-> HSO4(-) <-> SO4(2-) equilibrium).

Other common sources of CaCO3 are: washed and crushed eggshells, cuttle bones (from a pet store in the bird department), and crushed oyster shells (pet or farm feed store)."
-taken from Alkahest over at ST-

Now, this seems pretty straight forward, CaCO3 is superior because it is more soluble, less reactive, and less acidic, BUT! My question is regarding the SOLUBILITY when comparing gypsum, which is a powder, and crushed oyster shells, which are not all that soluble (excluding solubility on the molecular level because I dont know about it, actually thats what i'm asking about).

Can anyone shed ANY light on this?

Calcium carbonate has a basic pH whereas calcium sulfate is close to neutral. I don't have the specifics in front of me at the moment but in general one uses only a very small amount of calcium carbonate since too much can produce too high of a pH and interfere with growth. Many formulas I have seen use both the carbonate (smaller amount) and sulfate (slightly larger amount). These can help with yields but are not absolutely essential. So if this is your first grow you might be safer to do without them unless you have specific amounts listed. Might make a difference of say 10-20% in yield.

elphologist

Do you have a specific PH that works best for fruiting?

Just slightly basic - somewhere between 7 and 8. Not only does being just slightly basic help the mushrooms, it also helps inhibit mold growth since mold grows better in acidic environments.

I'm no expert, but I have grown before (both actives and edibles). I've hung out on the Shroomery before and they have a lot more details on growing mushrooms of all kinds. I'd recommend checking them out - even if you don't post you can still read the techs and learn a lot as I did.

elphologist