baking soda KH question - Page 2 - The Planted Tank Forum
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post #16 of 22 (permalink) Old 09-28-2015, 08:27 PM
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"Buffer Definition:
A buffer is a solution containing either a weak acid and its salt or a weak base and its salt, which is resistant to changes in pH." from Buffer Definition - Chemistry Glossary

The buffer we get with KH consists of a weak acid, H2CO3 (carbonic acid) and (X)HCO3, a salt that contains the conjugate base for carbonic acid, HCO3-. That buffer maintains the pH of the water at the value that corresponds to the KH of the water and the amount of dissolved CO2 in the water. It buffers against weak acids like tannic acid from sources in the water. It does not buffer against addition of more CO2 or more KH.

Just to clarify the chemistry a bit.

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post #17 of 22 (permalink) Old 09-28-2015, 11:36 PM
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Originally Posted by Ras View Post
thank you for the info! I was hoping to use something that was almost instantly water soluble so kh wont slowly rise between water changes. does potassium bicarbonate take more than a day to dissolve fully? the less fluctuations during wc the better and so I dont have to do more testing than I need to
Potassium bicarbonate dissolves very quickly.
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post #18 of 22 (permalink) Old 09-29-2015, 12:18 AM Thread Starter
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awesome. taking everything into account potassium bicarbonate sounds perfect for what I need, thanks again everyone
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post #19 of 22 (permalink) Old 09-29-2015, 04:54 AM
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Ditto- it does dissolve fast. I was simply being cautious in suggesting that you monitor a test batch to see if it was going to do something unusual.

The other materials that I listed in post 14, under the line, are slow, good additions to the filter if there is something in the tank that is slowly removing any of these minerals- For example, some substrates remove carbonates from the water.
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post #20 of 22 (permalink) Old 09-29-2015, 06:29 AM
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Potassium Bicarbonate buffer:

Make a 300g per 1 liter solution.

dose 30ml per 40 US gallons / 151 liters to raise KH by 2 degrees (dKH) = 36ppm

Recommended levels are between 2.8-5.6 dKH or 50-100ppm

This also raises potassium by 23mg per liter or 23ppm

*apply this dosing volume to the TRUE amount of water taken out and put back into the tank each week, and not the total tank volume! It is preferred to use RO/DI water. For unbuffered water or in the absence of CO2 injection, use 1/4 to 1/2 dose to avoid impacting pH. I run my tank at 3KH, 6-7GH, with a 6.6 pH.
And these are all really guidelines because each tank is different and we are not always consistent. So, always test the KH of your water when first getting down a routine. After a routine is established you can check every month or so to make sure you are still on track. Sometimes your KH can accumulate if you did a tap water evaporation refill, or dosed too much one week, so always monitor your KH, but truly in this situation it is alkalinity considering we are not using calcium bicarbonate or magnesium bicarbonate.

I hope this helps.

You can get potassium bicarbonate off of Amazon for super cheap, and it will last you a few years. They use it in wine production.

Keep your sleeves wet!

Last edited by DaveFish; 09-29-2015 at 06:49 AM. Reason: more info
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post #21 of 22 (permalink) Old 09-30-2015, 10:47 AM
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Originally Posted by Hoppy View Post
It does not buffer against addition of more CO2 or more KH.
Correct. Because both of these shift the equilibrium of the carbonate buffer.
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post #22 of 22 (permalink) Old 09-30-2015, 11:03 AM
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