Shell grit for Bio filter?

[anniefish]

Hi all,
I know some of you use oyster shells in bio filters, just wondering if I could use shell grit? It is broken up shells fed to poultry. Would it be too fine and/or too salty? What size drum is recommended and how much filter material does it need to have? I understand you just let the water flow in the top and filter through and then back to the tank. Any pointers?
Cheers, Ann

[GaryD]

Hi Annie,

I use oyster shells in my bio-filters and I think that they are probably ideal for the purpose in that they offer plenty of surface area for the substrate in which the nitrifying bacteria live, facilitate oxygenation of the water, they cost nothing and they may help in countering the naturally acidify effect of an aquaponics system.

The issues that I see with shell grit, is that the fish solids might cause it to clog over time and that it would not encourage oxygenation to the same extent as oyster shells.

Having said that, coarse shellgrit would probably make a great mechanical filter for the removal of fish solids. You would simply change it every week or two.....the used stuff could be given directly to your chickens (fish waste and all). A pre-filter of this type would be used immediately before bio-filter......it would probably sit on top of the bio-filter.

GaryD