can oyster shells be used as sand bed??

[BSHANE651]

i am trying to find out if crushed oyster shells can safely be used as a sand bed for a tank, the label says 94% calcium carbonate
which is the same stuff my base rock is made out of??
it is also one of the main ingrediants in almost all diy live rock.

i thought i read somewhere that it can release phosphates, if so can it be soaked for a few weeks, prior to using in tank after a few water changes??

i really do like the texture of it and it is far less costly than aragonite or crushed coral / shells, all af these are also calcius substances would they not also pose possible phosphate problems, thank you for your help..

[Randy Holmes-Farley]

For a chemical perspective, it is a fine material to use, but it is true that all natural calcium carbonate materials contain some phosphate. They do not all contain similar levels, however. I do not know how much those shells may contain. It may depend a lot on the purityof the water where they came from, and on whether all organic material was carefully removed.

[DonJasper]

IHMO - there is no 'substitute' for sand. And no need. I used 'sicila free playsand' from a LHS (Local Hardware Store). On the left coast there is a breed of Sand Lunatic that does pay heavy dollars for white sand. I used brown sand. I wish I could've found whiter sand, but not to degree that Sand Lunatic's go. I think that sand basically just sits there - same as all the rocks in the tank. If there is any difference - it's too far to the right of the decimal point to make up for inadequate flow, insufficient nutrient export and about zillion other factors for me to have noticed.

[Habib]

I tested some broken shells in the past and saw a huge increase in phosphate.

Atleast here in Holland, crushed shells are used in farms and they have to be heated to high temperatures before they are allowed to be sold.

The heating process might also increase the leachable phosphate fraction.

[BSHANE651]

WHEN YOU DID YOUR TESTING DID THE PHOSPHATE LEVELS DISICIPATE OVER TIME, OR WOULD THEY BE CONSISTANTLY HIGH??

[Habib]

Originally posted by BSHANE651
WHEN YOU DID YOUR TESTING DID THE PHOSPHATE LEVELS DISICIPATE OVER TIME, OR WOULD THEY BE CONSISTANTLY HIGH??

They were small scale experiments. The amount released in my case was so high that it would be highly problematic if used in an aquarium.


However, there are people who use it and I have not seen that they reported negative effects.


IMO, I would be careful. Since it probably does not cost much one can always buy some and test it for easily leachable phosphates just to be sure.