NaHCO3 isn't giving me the calculated KH increase


Jan 20, 2021

I'm trying to increase the KH of a small shrimp planted tank and it is not working as calculated. My tap water comes with a KH of around 0.5 DKH and I would like to increase it by 4 points. I'll list the procedure I'm using and would like your best guess as to what is most likely the problem.

I'm using NaHCO3 bought in a 1kg package, from a lab materials store;
I'm making a solution using tap water in a 200ml container and adding 5,6g of NaHCO3, it dilutes completely;
I weight the powder with a cheap chinese electronic scale with a 200g capacity and a 0.01g resolution;
Using a 30ml plastic pipette, basically a graduated turkey baster, I add 30ml of this solution to 7L of water, which is the volume of the water change;
I measure KH of the water change water using a test from Prodac with water volume that gives a 1 DKH resolution, the result is 2 drops indicating 2 DKH, half of what was intended.

Do you think the problem is the powder, the scale, the KH test, the math... or what?


Super Moderator
Staff member
Lifetime Member
Jun 20, 2016
Math checks out. Could it be that the water change water wasn't completely well mixed. Then I would look into having a KH test from another company and compare the 2 results.

You can calibrate the scale before every use, most of them come with a calibration weight. It may not be accurate to the 100mg range but wouldn't expect to be so much off.


New Member
May 24, 2022
South Dakota
Well, a great biochemist said one time never to use tap water because you never know what contaminates is in it. Always use distilled water.

I do, 100% in my tanks. No side effects and my chemistry is always the same.

Btw, What is your substrate, because your substrate has a big effect on those water parameters.

Maybe you need to do a biology experiment : take a few glass jars, and put a few inches of substrates of different kinds in each jar, fill them with distilled water. Wait one week, then test the water parameters for each different substrate. This is a test of how a substrate mixture effects the ph parameters (PH,KH) and I always suggest this to the serious hobbyist that wants a certain result so that they can start correctly with their tank setup.

Otherwise, you going to fight a loosing battle turning your tank in a chemistry set.