Ph Buffer Bicarbonate Of Soda

[Zante]

I am quite confused about some info I found on the net.

I was reading that adding bicarbonate of soda will buffer the ph, but not change it, to change it I'd have to use something else.

Ok... I am not a chemistry genius, but didn't bicarbonate raise the ph?
I mean, if what I read was true, I could put bicarbonate in my discus tank, and keep my ph buffered to 6.2 or thereabouts, but this doesn't make sense to me.

Did I read ##152###, understand ##152### or is it actually so?

 

[DevotedToDiscus]

Mate, bicarb will buffer the pH(I use it in my brine shrimp hatchery), and will raise it ever so slightly, unless you add too much. If you bake it to generate sodium ash, then it will raise the pH. To be honest though, and for your own peace of mind, it is better to buy a product specifically designed for the task in hand, rather than trying to save a few quid.

 

[Zante]

Oh, no, no intention of using it. I was just curious.

 

[DevotedToDiscus]

Oh ok.

...... I believe it has a pH of just over 8 at 10%, but that would be rather a lot to add. As a buffer it is ok, and I think some salty folk use it. Makes all my brine shrimp eggs hatch nicely

 

[TwoTankAmin]

Hardening Your Water (Raising GH and/or KH)
The following measurements are approximate; use a test kit to verify you've achieved the intended results. Note that if your water is extremely soft to begin with (1 degree KH or less), you may get a drastic change in pH as the buffer is added. To raise both GH and KH simultaneously, add calcium carbonate (CaCO[sub]3[/sub]). 1/2 teaspoon per 100 liters of water will increase both the KH and GH by about 1-2 dH. Alternatively, add some sea shells, coral, limestone, marble chips, etc. to your filter.

To raise the KH without raising the GH, add sodium bicarbonate (NaHCO[sub]3[/sub]), commonly known as baking soda. 1/2 teaspoon per 100 Liters raises the KH by about 1 dH. Sodium bicarbonate drives the pH towards an equilibrium value of 8.2.

From http/fins.actwin.com/mirror/begin-chem.html#altering

 

[Essjay]

Sodium bicarbonate should only really be used during a fishless cycle to raise the pH if it crashes and stalls the cycle. It gets removed with the big water change that's done just before getting fish. It adds a lot of sodium to the water, which isn't really a good idea when there are fish in the tank.

 

[TwoTankAmin]

It do not believe it puts Na into the water. Check your chemistry.

 

[Essjay]

Bicarbonate of soda is sodium bicarbonate, NaHCO3. It contains sodium so it will add sodium to the water.
Edit: to add that every 10g of bicarb added to the tank adds 2.74g of sodium.

I have a degree in chemistry. My husband has a doctorate in chemistry and my younger son is currently studying for a doctorate in chemistry. They agree with me.

 

[TwoTankAmin]

Are you sure it adds Na vs Na[sup]+[/sup]? What I have read indicates when you add NaHCO3 to water this is the result: NaHCO3 (s) → Na+(aq) + HCO3[sup]-[/sup](aq).

I read that when it is put into water, NaHCO3 dissociates to form a bicarbonate ion (HCO3[sup]-[/sup]) and a sodium ion (Na+).

I also read this:

There are many differences between the sodium ion and sodium atom.

The charge of the sodium atom is neutral, while the charge of sodium ion is positive(+1).

The sodium atom reacts with hydrogen gas and oxygen gas.

2Na + H2 --> 2NaH

2Na + O2 --> Na2O2

The sodium ion does not react with hydrogen gas and oxygen gas.

The conductivity of Na atom is very good, while the sodium ion is a poor conductor of heat and electricity.

The Na atom is found in pure form, while Na ion has to be combined with anions to form a stable compound.

from http/www.enotes.com/chemistry/q-and-a/what-difference-between-na-na-257647

Now I am about as ignorant re chemistry as you and your family are well educated, so clearly I must not be understanding things correctly. Could you please give me the layman's explanation for what I have missed or not understood as I am likely to have gotten it wrong.

I am a fresh water keeper and have no experience with salt water systems. But if one does regular water changes (on fw tanks), would that not prevent any serious build up of sodium? Further, I wonder that since many African rift lake cichlid keepers use baking soda for a diy buffer mix, why doesn't that harm their fish from a build up of sodium. (I know that rift lake water naturally contains some levels of sodium as well as sodium chloride.)

To quote Mr. Gumby from Monty Python "My brain hurts."

 

[Essjay]

I must apologise. As a chemist, when I say that it adds sodium to the water I automatically understand that as meaning it adds sodium ions to the water. Saying just sodium is a form of shorthand. I tend to forget that non-chmists won't understand my shorthand. Like, as a chemist I would use the word proton instead of hydrogen ion. That would totally confuse a non-chemist!

Just to clear things up: sodium bicarbonate is a salt (in the chemical meaning of the word). All soluble salts dissociate into their ions when dissolved in water. In this case sodium bicarbonate dissociates totally in water to give sodium ions (Na+) and bicarbonate ions (HCO3-). Bicarbonate of soda does not add sodium metal to the water, it adds sodium ions.

But sodium ions are not terribly good for fish, which is how I should have phrased it before. Most natural water sources contain either very few minerals (soft water) or a lot of calcium and/or magnesium ions (hard water). Very few natural sources of water contain much in the way of sodium ions. Adding sodium ions (as bicarbonate of soda) to the tank creates tank water that fish have not evolved to cope with.

Edit - I should have said most FRESH water sources. The rift valley lakes are the exception to the rule. And marine water is different again.
But most people who want to add buffer in the form of bicarbonate have soft water, which is why their pH crashes so easily. Soft water contains very few ions of any sort.

 

[DrRob]

Adding metallic sodium to a fish tank would certainly be interesting to watch though.

 

[Essjay]

Yes, FLASH!!!! BANG!!!!

Not as bad as adding potassium metal though.

 

[StandbySetting]

Try Caesium, much more fun.

 

[DrRob]

Put the alkali metal down, and step slowly away from the fish tank.

 

[Essjay]

But if one does regular water changes would that not prevent any serious build up of sodium?

I forgot to answer this part.

If you have soft acidic water and want to keep fish like discus, your water is perfect for them. But the chances are you also have very low KH, that is very little buffering capacity. It would be very tempting to add something to the tank that would increase the KH without affecting the GH, such as bicarbonate of soda. But you wouldn't just add it once, you would add it to the new water at every water change to maintain the KH level resulting from the first addition. Depending on how accurately the fishkeeper measured the amount he added to the new water, the sodium ion concentration would remain constant (or more likely, fluctuate slightly with each water change)