Why do some people filter water through Oyster Shells and/or bits of Coral

[mailoo]

I have seen in many sumps at LF shops here in thailand that they are trickling the water through a rather large amount of oyster shells and then through some coral peices (not crushed coral, larger than that).

Why??

Does the coral peices help with Calcium levels?

I am a bit lost... and i think i want to build this into my sump (i am making a custom one)

[JeRmZ]

the coral pieces I'm not sure, but maybe for buffering reasons.

and if the oysters are live then maybe they actually help with "filtering" the water. Or is it empty shells?

My guess .... I could be wrong!

[Amador]

They're using the LR rubble / oyster shells in a bubble tower. Basically you put some rubble inside a piece of large-diameter PVC with holes in it, and the bubbles from the ride down to the sump rise, and water is forced out the holes in the pipe.

[AngeloM3]

doing that is kind of a "natural" filter

same thing if you had a regular filter on your tank or canister

[AngeloM3]

also.... its said to help reduce micro-bubbles.

not sure if thats true or not

[hairymushroom]

They use shells / coral skeletons as a surface area for bacteria, the same can be done with bio-balls.
I doubt the coral skeletons have effect on calcium levels.
As for incorporating that type of setup into your sump, i would advise against it as the shells/coral will trap detritus and basically add unwanted nitrates back into your system in the long run. Best would be to use that space for a refugium/DSB.

[mailoo]

A DSB in a bucket is planned... a really big one...

As for a refugium... i have not even looked into them at all yet ... i guess i should... people always seem to have them.

[mailoo]

O and yes the oysters are just shells... not live ones.
Can buy them easily in this town.

[hairymushroom]

Skip the shells, go for a refugium with macro algae, preferably chaetomorpha.