A recent answer stated that egg shell can be crushed and used as a calcium supplement in Do-it-yourself food. This got me relating it to crushed coral, which is commonly used as a substrate.

I've crushed one egg shell and I noticed they get very fine, and have a nice bright white color, they also are denser than water and so they sink down, as a substrate should. Not that I'd go through the elaborate trouble of crushing a big number of egg shells to make a substrate from them, perhaps industrially it'd be a good idea, since they're cheap and perhaps non-toxic paint can be applied for decoration. This is all basically theoretical, though it might be already applied without my knowledge. This also is a solution for pets that are known to swallow substrate and can be used as a mean of avoiding impaction.

Is it safe to use egg shell as a substrate for aquariums and terrariums?

  • I would think it would encourage bacteria growth. Commented Aug 10, 2014 at 5:06
  • @Jeff-InventorChromeOS Perhaps I'm really not sure, but what kind of bacteria? Nitrifying bacteria , for instance, are rather expedient for an aquarium since they get rid of ammonia.
    – Mozein
    Commented Aug 10, 2014 at 9:10
  • I don't know. I'm just speculating, anytime you add organic material to your aquarium, it's going to encourage something to grow. Commented Aug 10, 2014 at 9:17
  • The shell is just more or less inorganic calcium carbonate. Making sure you get the lining out of there before crushing it would be hard.
    – Oldcat
    Commented Aug 12, 2014 at 21:30
  • @Oldcat actually, removing the lining was quite easy. After u crushed the shell, I put it in a cup with water, so the lining floats while the actual she'll remains. From then I just put the water out along with the lining, I repeated this just to make sure and all the lining was gone.
    – Mozein
    Commented Aug 13, 2014 at 11:20

2 Answers 2


It depends on what you want to have in your tank. If you are housing fish that need a very high pH (cichlids), then it might work.

All other fish will probably suffer because the shells are either too sharp or because the pH will become too high.

Most people are even trying to lower their pH so adding egg shells will definitely not help with that.


A better option is diatomaceous earth. It's crushed seashells; you can buy it at any pool supply store and it's non-toxic and super fine. I have used it many times. I even put it on my dogs and on their bedding. It can even be used in fish tanks, it's all natural and non-toxic. I would check into that. As far as the egg shells, I'm not sure about that one. Hope that helps.

  • Diatoms are silica, there is probably some calcium mixed in. Commented Sep 30, 2020 at 15:21

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