Ph down buffer.

[Kelvin12]

Hello all,
I have been reading a lot of previous posts about Ph fluctuations and not chasing it with water thats on the acidic side. However I have been using ' Ph down' a few times and that reduces it but then its crept up again to well above my desired / recommended levels 5.8 , 6.0 quite quickly. I have been using this product, ' Ph down ' where the active constitute is Biphosphate. In addition so far I have been using quite a lot of peat and numerous IAL. Everything seems to stabilize for a bit but soon creeps up to around 6.8, 7.0 mark. I am using remineralized RO and thats keeping the TDS quite well within recommended levels .
I have PRL and CRS shrimp.

 

[dw1305]

Hi all,

I thought HCO3 were very soluble salts (are they ?)

More than soluble, they only exist in solution as bicarbonate HCO3- ions.

I.f so, where the excess of undissolved salts in buffer system based on carbonate come from ?

The undissolved carbonate (usually as calcium carbonate (CaCO3)). Have a look at <"Ocean Acidification">, this is sea water, but the carbonate bit is relevant to any hard water (fresh or saline).

cheers Darrel

 

[Cédric]

The undissolved carbonate (usually as calcium carbonate (CaCO3)).

How comes carbonate is not visible when undissolved ? Are quantities too little ?

 

[dw1305]

Hi all,

How comes undissolved carbonate is not visible when undissolved ?

It could be <"carbonate (CO3--) ions">, but only at high pH levels. The form <"the TIC takes is pH dependent"> and the pH is dependent upon the nature of the TIC, they are in a dynamic equilibrium.

You can also get a very fine dust of calcium carbonate (CaCO3) particles, you can see this when you add a <"soluble carbonate"> to water which is already saturated with calcium (Ca++) and bicarbonate (2HCO3-) ions and then CaCO3 precipitates out via <"the common ion effect">. You could still have an "excess" of HCO3- ions in solution, but as soon as you added a multivalent cation (Ca++, Mg++ etc) then insoluble carbonates will form, with CaCO3 precipitating first, because it is slightly less soluble than magnesium carbonate (MgCO3).

Carbonate solubility is controlled by the level of dissolved CO2, they are the weak base and weak acid in this pair, as temperature declines and CO2 concentration increases more CaCO3 will go into solution.

Because of this you can potentially remove all the carbonate ions from solution, by converting them to CO2 with an acid addition. This is why you get shell attrition in snails in high tech tanks, their shells are eroded by the extra carbonic acid (H2CO3) from the higher level of CO2, The H2CO3 disassociates into a proton (H+) and a bicarbonate ion (HCO3-). When you turn the CO2 off the 2HCO3- and Ca++ ions will come back out of solution, but not as part of the snail shell.

This process is what happens, much more dramatically, when you drip hydrochloric acid (HCl) onto limestone (CaCO3), and get CaCO3 + 2 HCl ---> CaCl2 + H2O + CO2 and as you can see you've converted some of your carbonate to CO2.

cheers Darrel

 

[dw1305]

Hi all,
I should have put a <"buffering link"> into the previous post. I think <"buffers & buffering"> are quite a difficult subject area, if you aren't a chemist (and I'm not). A good example of "buffering in action" is a drop checker <"CO2 MEASUREMENT USING A DROP CHECKER">.

It is partially the conceptual difficulties <"around pH and buffers"> that has allowed, <"less than scrupulous">, vendors to sell a whole range of products that have simultaneously <"no practical application"> but which do exactly <"what they say would on the label"> (below).

............. Converts carbonate alkalinity (KH) into available CO2. Contains no phosphate

"............. Converts carbonate alkalinity (KH) into available CO2........" is just <"pure genius">. It is a <"kills all known germs. Dead"> for the aquatics industry. Universally true for "acids" (any acid) & all "sodium hypochlorite bleach" respectively.

Because of this you can potentially remove all the carbonate ions from solution, by converting them to CO2 with an acid addition.

The safety data sheet for "Seachem Acid Buffer" doesn't tell you what compound(s) it contains, but it does say

Proprietary mixture of salts.
The identity and weight of proprietary, non-hazardous, main ingredients are withheld as a trade secret. Decomposition products can include and are not limited to: Sulfur Dioxide, Carbon dioxide, Alcohols, Ethers, Hydrocarbons, Polymer fragments.

Which, combined with "contains no phosphate" makes me think that it might mainly be <"sodium hydrogen sulphate"> (NaHSO4)* based, which would have the dual advantages of both lowering pH and being a very cheap chemical to buy.*

*But not <"actually a buffer">.

cheers Darrel

 

[Cédric]

Hi Darrell,
Difficult subject...True. I start from Ground Zero but I'm learning little by little (trying to learn at least !!). Your answers are another bricks in the wall of my knowledge. Thank you very much. Much appreciated.