Backyard Aquaponics
A place to discuss aquaponics

I've read where backyard systems have used bags of oyster shell to buffer their systems but I was wondering what commercial enterprises do. Do crushed oyster shells in the sump scale up enough for a large system?

Then I got to thinking, exactly how does this work? Is the lower acidity breaking down the calcium carbonate into calcium chloride or is it the CO2 from the fish breaking it down into calcium bicarbonate? Maybe a measurable mixture of both?

Reef aquarium enthusiasts sometimes use calcium reactors where CO2 is mixed with a fluidized container of calcium carbonate to release calcium. Do these have any application in commercial aquaponics?

Most people would probably be using shell grit... crushed shells... rather than oyster shells....

And no... a commercial operation wouldn't bother trying to control pH buffering with bags of shells


Fish respire ammonia.. not CO2... and the acidity disassociates the Calcium and Carbonate... which reassociate/disassociate into various other forms... but not into Calcium Chloride...


In its most basic form, a calcium reactor is simply a container filled with calcium carbonate (CaCO3) media... over which aquarium water is passed with the addition of carbon dioxide....

Adding carbon dioxide lowers the pH of the water, making it acidic, and dissolving the calcium carbonate to provide the aquarium with calcium and alkalinity....

The same process is essentially taking place in an AP system... where nitrification lowers the pH of the water.... etc... but ultimately consumes the carbonate alkalinity as part of the process...

Again... they probably don't have a commercial application.... other forms of more immediate, and controllable pH buffering would be applied...

Reef aquaria utilise them... to replace/provide for the Calcium sequested by the corals by growth...

Rupert, thank you for your insightful response.


I would think that would be a matter of location. All the feed stores here carry oyster shell grit at $US 0.20/lb. I've never seen a local source, retail or otherwise, for a shell grit that wasn't oyster shell. We are located in the mid-Atlantic area of the US and this is a commercial oyster fishery.


Would a different product be used or would it be the same product with a different delivery method or constitution?
I'm not an argumentative sort, but I believe that fish do respire CO2 in addition to excreting Ammonia from their gills. In fact, the aquaculture course at the University of Arizona teaches that for every gram of O2 that a fish consumes, 1.38 g of CO2 is produced. They also have a formula to calculate total CO2 produced daily as a result of respiration, combined with biomass, feed rate and DO:

(see http://ag.arizona.edu/azaqua/ista/ISTA7 ... Design.ppt)


That's what I guess I'm trying to get my head around. What do you suggest as being the solution in a commercial environment?

I realize there has been some argument as to what a commercial system is. I like the concept of looking at a 4 tank DWC system as a node and deal with them independently. It should matter not if you have one node of 20. For argument's sake, let's assume 4-1,500 gal tanks and 16,000 gal of DWC trough for a total of 24,000 gal US.

Again, thank you for your response.

Shell grit is shell grit... it doesn't really matter what shell...

I made the distinction between the "grit" and oyster shells.... because it's often suggested in AP to use oyster shells... as a whole shell....


Various "BiCarbonates", or "Carbonates"... principally Calcium/Potassium... (even Sodium)... could well be used.. but commercially other compounds such as Calcium Hydroxide (CaOH)... or Potassium Hydroxide (KOH)... would be more commonly used...



You're right...Don't know where my brain was when I posted that.... indeed CO2... primarily as a waste...from metabolic processes... feed protein conversion... is passed back over the fish gills... by counter flow...

Forming carbonic acid... and subsequent disassociation into a bicarbonate ion and a hydrogen ion... then disassociation of the bicarbonate ion into a carbonate ion and a hydrogen ion...

The "released" hydrogen ions lower carbonate alkalinity.... the ability to buffer pH... hence acidification...

In a commercial application... Carbon Dioxide stripping processes would probably be employed... most commonly by "off-gassing"....

And alkalinity addressed as above...

I guess it would be simple enough to borrow another item from reef aquaria, kalkwasser reactors. Heavily mixed calcium chloride dispensed at either a calculated rate or via a pH controller. Do you see any problems with that?

Kalkwasser reactors use Calcium Hydroxide... hydrated lime, also known as brickies lime....

It's the suggested pH buffer for use in AP.... just grab a bag from your local hardware store...

Sometimes Kalkwasser reactors utilise Calcium Oxide.... both compounds are strong bases and should be used with caution when adjusting pH...

A pH doser would be a consideration in a commercial system... but you'd have to make sure it was bullet proof reliable....

Rather than looking to an aquaria system... you would be better off looking toward an aquaculture or hydroponic system...

I was thinking more of the method of delivery, not the ingredient. Calcium Hydroxide is a prohibited item according to OMRI (U.S. Organic code). If Calcium Chloride could be provided in a fine enough powder, I'm assuming that would be the ticket.

As for potassium, I can't find a water delivery method that is OMRI approved. The only thing that seems available is foliar application. Might be ok for treatment, but burdensome for prevention.

Calcium Chloride isn't a pH buffer... and AFAIK isn't used in Kalkwasser reactors anyway....

Not sure what the water delivery method would have to do with any organic approval... ... surely it would be more about the actual input rather than the delivery method...

Oops, I meant calcium carbonate (fine ground oyster shell). The delivery method wasn't the issue, but calcium hydroxide is.

What I was meaning to imply, using a kalkwasser reactor, to deliver calcium carbonate or something along those lines... is that what organic commercial outfits use?