Hi All,
I am planning to use crushed oyster shell over an undergravel filter as a secondary biological filter system for my bimacs (this will be in a separate water conditioning tank; I know about octopus disrupting UG filters by burrowing!). Will crushed oyster shell from feed supply companies (cheap and readily available) be of sufficient quality or do I need to get it from a mycological supply company (more expensive and harder to find).
Thanks in advance for any advice!

I know nothing about your question, but I'll say :welcome: to hold you over until someone else chimes in. I seem to remember someone at the NRCC was using an oyster shell substrate, maybe gjbarord or marinebio_guy?

Are you planning on using it as a calcium source for the water? You'd be better with aragonite if you can get some?

It's not especially as a CaCo3 source; primarily as a substrate for bacteria to act as a bio filter. I think I am now feeling confident that feed-grade crushed oyster shell that I have thoroughly rinsed in RO water, sterilized in my oven, and then cooled will be fine to put into my tank, and left to cycle. Is anyone horrified by this idea?

Oyster shell works good for bio. filtration and aids in buffering the water, but it is usually set up in the filter (not the tank itself as for best results you need it 3-4in deep). For most small octopus tanks with undergravel filters we would use crushed coral or pea gravel as a substrate.

Wonderful; thanks. I'm actually going to put the oyster shell in a separate water conditioning tank (without animals) so I can use a depth of 6 inches or so.
This has been my first thread on this site and I really appreciate all the responses. You have a great community here, and I'm very pleased to have joined in.
Have a great weekend everyone.
Lene.

In my experience, crushed oyster shell has worked the best because of all of its different properties. Sounds like you will have a very nice setup.

Greg