Backyard Aquaponics
A place to discuss aquaponics

In my 50l micro system I've placed a handful of broken egg shells (with membrane removed) in a cloth pouch, under the pump outlet on top of the gravel. For ph buffering of course. After a few days, if you hold the pouch close to your nose, it smells pungent (like onions or garlic maybe). How does this happen?

Replacing the pouch and egg shells, the smell comes back in 3 or 4 days.

Details: The pouch is always wet. I can easily squeeze out several 10s of drops of water. Flood and drain setup. Pouch is on top of gravel, so receives sunlight (very very bright (summer)) from 2:30 pm to sunset.

Try shifting it to under the water return back to your sump or tank.... it'll be out of the sun most of the time that way as well....

Don't know if the effect of the sunlight and/or periodically drying out affects the buffering ability, but as that's what you're really wanting ... and wanting it in the tank water, then IMHO you're be better off...

Otherwise most of any calcium/carbonates released will be directed into the growbed... by the time they make it into the tank water you may have lost any benefit.

would suggest removing the membrane, it is organic making it susceptible to rotting (breaking down).

i think the membrne has been removed.

i agree, place the puch under the water return. they only work if water can flow over / through them.

It does not dry out :

I like my bacteria as much as or more than my fish. I can buy more fish if they die but I can't cover all my gravel with biofilm if it's gone!
By the way, buffering is due to CO-3 (carbonate) ions in solution in the water (KHardness KH) . So the buffering of water is the same whether in growbed or fish tank.

It is removed But yes, some of it maybe still present. (very little amounts of it)

It is under the pump outlet:

Ok I have an idea.
Usually the bad smell of H2S (hydrogen sulphide gas) is called the "rotten egg smell".

Also I said : Even onions and garlic have sulphur in them.

Maybe it is due to some sulphur or something in the egg shell?

Has anybody here ever used eggshells for ph buffering? Did it smell pungunt for you too?

I recall that when I put egg shells into a mesh bag in my system (before I got any sea shells) that they did take on an odor. I'm not sure I would have said like garlic but I am sure it was something rotting. I didn't remove the membranes. I usually let the shells dry out for a few days before breaking them up.

I also know that there is an odd odor (not really a rotting odor but strong and odd) when I grind up egg shells in an old coffee grinder. I grind the egg shells for the worm bin. The washed sea shells have taken over buffering in my AP system.

Perhaps a bag of shell grit from a feed store will serve you better if the smell from the shells is a problem.

Another idea might be to stick the shells in the oven or toaster for a bit before adding them to the system.

although i disagree with the carbonates being released into the growbeds quote...............

careful with the CO3 in solution comment...............

CaCO3 is very INSOLUBLE

i would assume that the buffering provided by it follows the equation: 2HCl (aq) (for an Acid example) + CaCO3 (s) -->> CaCl2 (aq) + H20 (l) + CO2 (g)

adding CaCO3 into the water is unlikely to create a large KH shift because it is not in solution to any great degree like for example sodium bi-carbonate would.

I studied buffers as a small part of a chemistry course in my pre-undergraduation time. Yes it is very insoluble, I'll put in another post explaining what I actually meant.

Carbonate ions, CO-3, are very feebly soluble.

H2O + CO-3 {as part of a solid salt, say CaCO-3, calcium
carbonate} <=> CO-3 {dissolved in water} + (H+) +
OH-
Comments are in {}
The <=> means an equilibrium reaction. Meaning, the reaction goes either way
(left to right and right to left) and eventually settles down. There is
a certain ratio of the rates in each direction, which is constant for
other conditions being constant.

Of course CO-3 in solution is very less, but not zero. It is an
equilibrium reaction.
If I write the concentration of any substance A as [A], then this
equilibrium ratio is given by:
ratio = [H+][CO-3 in solution]/[CO-3 as solid salt][H20]
(above the division bar we have things on the right side of the equation, below we have the other stuff).

Concentration of [CO-3 as a solid salt] and concentration of water itself will now be removed from the ratio equation because

• It's funny
• CO-3 as solid, and water are always fully available for any reaction so things are not going to depend on them, as long as they are present.

This equilibrium ratio is constant.

By the way:
pH is the negative of the logarithm (log) to base 10, of H+ concentration [H+]

Also the log( product of two things) = log (one thing) + log (the other thing)
and log( one thing / another thing) = log (one thing) - log (the other thing).

Why log : log(10) = 1, log (100) = 2, log (10000000) = only 7! We can thus talk about huge numbers using only small numbers, if we use its log. [H+] can be huge. We can also talk about very small numbers with the log. (log(0.0000001) = -7) So pH = - log([H+]) gives us small nubers we can easily talk about like 6.5 and 7.5 instead of 0.000000316 and 0.0000000316.

So, coming back to it:
In the ratio equation, finding logarithms,
log (ratio) = log([H+]) + log ([CO-3] in solution)
or log (ratio) = -pH + log([CO-3 in solution])
Or ph = - log (ratio) - log([CO-3 in solution]).
How does pH vary now?
As we think so , CO-3 is feebly soluble in water, so that term with it is going to be very small.
The ratio is constant, so pH = mainly - log(ratio) , minus a very small thing
ph = mainly - log (ratio) which is constant.

Now you know why ph is quite constant with a buffer solution!

I googled "egg shell compositon sulphur".

Eggshell happens to be 97% calcium carbonate. The rest is calcium phosphate (phospates yay), magnesium (yay) potassium (yay) and a little (0.1%) sulphur. And some organic stuff too.

The sulphur must be giving strange smelly products.

Ah thanks for the confirmation!
I don't care how it smells for me, but is it bad for the fish or bacteria? H2S gas smells similar and is supposed to be bad(toxic?).

If it does turn out to be bad, we must be advocating against the use of eggshell as ph buffer. Remember all this pungent stuff is going into solution into the system!