Ways to add calcium into substrate

[Exoskelos]

I like to think I do pretty well with keeping a fair amount of nutrient in my millipede substrate, but there's always room for improvement. Anyway I'm wondering how to keep stable calcium levels in the substrate. I had crushed up an entire cuttlebone into dust and mixed it in originally, but I have twice as much sub now.

There are a lot of millipedes in the enclosure, and I want to make sure they stay healthy, especially the small ones. I've got eggshells crushed and mixed in, but the pieces are fairly large, and I'm uncertain they will be eaten. I might mix in some of those cricket water crystals, I have a container of it that comes with calcium in the crystals.

I think mixing eggshells with vinegar to dissolve and use in a sprayer will work, its normal use is for gardening. With what I've read, the reaction between the shells and vinegar neutralizes the vinegar, but I still want to be careful.
Any other methods out there to ensure proper calcium distribution?

 

[pannaking22]

They should nibble on the eggshells, so I would just crush/grind up more dried egg shell and mix it in.

 

[Exoskelos]

They should nibble on the eggshells, so I would just crush/grind up more dried egg shell and mix it in.

Ok. I'll make sure to grind them up really well once I get enough. I've found a bag of worm growth formula that is a powder, has calcium and essential nutrients. I've used it before and it works wonderfully, considering millipedes are basically fancy worms with shells. They're not really worms, but it still works well.