crushed snail shells and chemistry

[andruboz]

my puffer recently moved to the new 125. he left behind quite a mess in the 55. tons of crushed snail shells. no meat left on them but they are probably breaking down/decomposing in the water. its been months since i checked kh and dh. i dont think i wrote down what it was months ago anyway.
i did see quite a bit of bubbles come up when i thoroughly aggitated the gravel [while syphoning]. but i dont think those are the deadly toxic anerobic gasses because ive seen fish poke around and raise bubbles while foraging and they dont seem affected. i aggitate enuff for it be released in small bubbles so there wont be a huge pocket of this stuff forming as long as i stay on it.
i just wonder if some element in the shell is attaching itself to an oxygen molecule to create this phenomenon.

i could compare it to the kh and dh of another tank that hasnt had the puffer in it. these shells arent light enuff to syphon up. not sure how iam going to seperate it from the gravel if i have to.

[RTR]

As a puffer fancier, I have multiple tanks with that situation. After 10-15 years of feeding snails, I figure some of my tanks are about 1/3 crushed shell substrate. When I Python, the crushed bits sort out atop the gravel in the siphon tube, but they do not get pulled out. It does support the hardness a bit - I don't remember the numbers, if I get a chance I'll test later and repost.

I do not see bubbles coming from the substrate, so I'm not sure that is related - at least judging by my tanks.

[a_free_bird73]

Technically, shells don't decompose (only organic matter does), If all what is left is shells, then they will slowly dissolve and give a high kH and pH. They will however stop dissolving at pH >~8.

Would make an ideal cichlids tank but other than that, it is not worth the effort. Just get clean gravel. If you really have to, you can treat the gravel with a strong acid to dissolve the shells, but that depends on the type of gravel you are using..

The bubbles could be trapped Carbon Dioxide. Nitrifying bacteria produce many acidic compounds which slowly help the shell to dissolve producing carbon dioxide gas...