Pulverised egg shells are good- and cost nothing! Grind with coffee grinder or mortar and pestle until you get a fine powder.

This is my first post on the Vermicomposting forum. Although I know nothing about this topic I do something about limestone, like anything with calcium it raises the pH. Agricultural lime is Calcium oxide.
I know the action of earthworms raises the soil pH. Tell us again why you want to reduce the pH???

Apparently, mites favor an acidic medium, so I want it to be more alkaline. I just want less mites. Before, they appeared to be taking over! Pot worms, which are downright gross, also like an environment high in acid.

Hi. We purchase our Calcium Carbonate at a local feed store. We buy in bulk though. It is crushed oyster shells and very safe to use. We periodically sprinkle it on the bedding or mix it in when we are "fluffing" them.

Sam.. Chevere wants to lower the acidity. That is raising the pH. Although I think it is probably a waste of effort. You'd probably find the pH is well within normal range..compost tends to neutralize on its own. Crushed eggshells as great either as grit or a calcium additive, but I wouldn't go out of my way.

I hate mites too. I found them in my hortensis bin after i added alot of water and moved it inside because I figured it was just too hot for them now in the garage. I left my fetidia bin and my BSF bin in the garage where they seem to be doing fine.

If you have both mites and potworms the bin is far too wet.

Go ahead and add crushed egg shells but also add dry paper shreds to dry out the bin. And cut back on the food until the problem is solved. Greater air flow also helps.

IMPORTANT - Sam md z7 - Please note an important correction - Agricultural lime is NOT Calcium oxide (CaO). Calcium oxide, commonly called quick lime, is highly alkaline, very corrosive and DANGEROUS and should never be brought anywhere near the worm farm.

Agriculural lime is actually calcium carbonate CaCo3 which is much milder, as it is just groundup limestone or chalk. Ground sea shells, eggshells or even marble also contain Calcium carbonate and are safe to use with your worms in smallish quantities.

If limestone (Calcium carbonate) is roasted in industrial kilns - then it converts to quicklime (Calcium oxide)and in the process becomes dangerous.

Here is a link that might be useful: Worm Terms