Seashells in a Freshwater Tank?

[rallycat]

Quick question for the more learned members here: Can I put seashells I found on the beach in my freshwater (29 gal) tank? I've soaked them in fresh de-chlorinated water then boiled them. Is there any way they can become toxic to the fish? Any help would be great, thank you!

 

[madasafish]

Seashells are literally CaCO3, calcium carbonate, with very little else. This means that they dissolve slowly as calcium (2+) ions and carbonate (2-) ions. Both of these are safe for fish, and beneficial for plants. Depending on their size and number, they may increase your water's pH and KH (carbonate hardness) a tiny bit, but I'm guessing that this won't happen to a noticeable extent with shells, as it does with large limestone rocks.

If you have boiled out any organic matter and other waste that might have been in the shells, and have tried your best to get any gunk out of them, they should be absolutely fine. I'm about to put two abalone shells in my breeder tank in a few days to make the fish a breeding space...

 

[rallycat]

Thank you so much for the help! I'm off to set up my new decorations.

 

[Menagerie]

I have a ton of seashells in my Mbuna tank. The smaller fish hide in them.