Backyard Aquaponics
A place to discuss aquaponics

Ok, so by this stage everyone knows that calcium carbonate is THE stuff to incorporate into your systems to buffer the ph to pretty much 7.5ish

BUT did you know that there were 3 different crystaline forms of calcium carbonate?

i'll list two.

Calcite: lime stone, most marble, sea shells, oyster shells, egg shells...........
has the desired ph effect that we want

aragonite: Corals, crushed or otherwise ...............aragonite will dissolve at a much higher ph 8+ which is why it is preferred in marine aquaria.

Here is a little cut and paste from a marine Q&A site

In the ponding community, it is suggested to mix a cup of plaster of paris and place it in the pond to buffer the PH. Is plaster of paris the same material you are writing of here, Steve?

Nope, but now you've got me interested in something else!

i assume this is what you're talking about?

http://www.koivet.com/html/articles/art ... icle_id=76

plaster of paris seems to be a either pure calcium sulphate, or as the link above stated a mix of calcium sulphate and limestone.


Lime stone is what i am talking about, along with any other sea shell or egg shell. it will slowly buffer your water to around 7.5

calcium sulphate seems to have a ph when dissolved in water of about 6


I still prefer the no-overdose fool proof method of using calcium carbonate aka calcite aka limestone

the calcium sulphate / plaster of paris may be an interesting choice if your aquaponics system becomes deficient in sulpher

What about drywall? I have a lot of that.

I'd be worried about what else is in drywall

People sometimes use gypsum to increase calcium in soil without increasing the pH. I understand it can be useful for improving certain sodic clay soils.

How likely is it that a AP system would need any extra sulphur? Doesn't the iron that most people use have some sulphur in it?

steve, Is it ok to use limestone as growbed filler?

Hi brycicles, welcome to the forum.....

As you can see, the discussion of using limestone or similar compounds is taking place in the context of adding a "carbonate" source to our AP systems as a "buffer" to acidic tendancies...

So yes limestone would be OK for a growbed media... IF and ONLY IF you were starting (or topping up) your system with an acidic water supply or if your system water was perhaps near nuetral and tending toward acidic as the system aged.

Would depend somewhat as well on the actual size of the growbed and the relative volume of the system.....

A large limestone growbed volume compared to a small fish tank volume would probably result in too much of a buffering effect.

Probably better off just adding a carbonate source (like those listed) which can either be added in small amount when required or one (like shellgrit etc) that dissolves and releases carbonate when required....

Shellgrit etc does this perfectly as it will only dissolve when the system pH tends towards acidicy... then it buffers to a point where the pH results in the solubility dropping off towards nothing.... i.e the point where it's no longewr required to buffer further anyway.

limestone also has magnesium carbonate, so it would be a sounce of magnesium.

bry, why dont you setup a small 60lt tub with crushed limestone and circ. the water in it for a few weeks. would give you an idea of the PH to be had.

if its approaching the high end of 7 (say 7. then you may not want to use it exclusively...................

I see people talking about shell grit and different products that can be used to buffer the pH but can good old dried and flattened egg shells be used? I often grind up egg shells as grit for the worms but we go through more egg shells that the worms need. Should I save some aside to put in the AP system?

yep, more detail shortly

I have added eggshell to my AP system. Also oyster shell grit like is used for chickens, and broken shells from the beach.

oh, i was going to post more.................

i find that if you can remove the thin "skin" i'm sure hit has a name from the inside of the egg and dry it then it crushes up beautifully.

When I cook an egg on the barbie (or more often several) after I have cracked it onto one of the solid plates to cook - I put the shells on the grill plate. Although the burner is not on under the grill plate at the time, there is still pelnty of heat. Dries the egg up quickly and by the end of the barbie the egg will be in a state where it crumbles easily . No extra work, no extra energy :-)

good stuff i still have a whole shopping bad full frozen from when i used to collect them