Best thing I have found is get a bag of aragonite sand, (commonly sold
as Southdown or Old Castle Sand) at Home depot. Add a small amount of
portland cement and make a few aragonite sand/ portland cement shapes
or forms that can be used to place plants on instead of bricks, or
some shape that is suitable to sink or place in the pond. Make rthis
a really dry porous mix so its more like a sponge than a concrete
casting....., even alowing holes etc tob e through it. Once cured, you
shoul dbe able to pour wate ronit and have it permeate right through
the shape you cast...If it runs off its not gonna work as well. It
needs ot be sort of like swiss cheese or a sponge......very pourus and
a dry mix is what it takes to achieve this density. ONce PH is lower
it starts to dissolve the aragonite sand which raises the pH. It has
to be the type sand listed in this post as regular silica based sands
will not work at all. If in doubt, carry some white vinegar with yu in
a bottle with a eye dropper, and put a bit of vinegar onthe sand. It
should fizz and bubble........if it done snot , its not the right
sand......
Plaster of paris may work but it does not really do much to correct or
buffer in sufficien t time without allowing wide swings in parameters
to occur. Sufficient aragonite (calcium based) sand wil lbe a suitable
buffer, but it may take considerably mnore than you really think it
needs to maintain a suitable buffer for stabikizing PH. Why do you
think its such an important factor in sal****er tanks to use aragonite
sands and calcium based liverock...its what really sets and holds the
ph and calcium levels.

On Sat, 03 Jun 2006 09:55:30 -0400, Hal wrote:
On Fri, 02 Jun 2006 21:10:58 GMT, "Snooze" wrote:

Has anyone here had much experience with using oyster shells to provide
calcium for aquatic crustaceans and to buffer pond pH? Primarily any
difficulties with general hardness because of the extra calcium? Obviously
I'll have to keep a closer eye on the pH now, and possibly deal with calcium
buildup at the waterline.

Otherwise any other suggestions?

I use garden lime because it is cheap and available, but the KH stays
very low and the pH usually stays around 7.8 to 8.2. After a rain
the KH will sometimes drop so low it is a bit frightening, but when
the pH drops below 7.8 the lime begins to dissolve raising the KH and
pH. I suppose the oyster shells would react about the same.
General Hardness has never been very high. I used plaster of Paris
to raise the GH several times, but it never seems to make any
difference to the fish that I can see, so I have grown lazy and ignore
it.

Regards,

Hal