Re: Water chemistry assistance

From: John Lobingier <jlob at wpa_net>

> I am adding 1/4 tsp of baking soda per day.  This is a 55 gallon tank.

I use the rule of thumb that 1 tsp per 50 liters will increase the KH 
by 4 degrees. 

1/4 tsp in a 55 gallon tank should increase your KH by about 1/4 to 1/3
degree.  Keep in mind that both "1/4 tsp" and fractional dKH are hard
to measure accurately. 
> Here are my water values from 1 or 2 (?) weeks ago.
> pH 6.0, KH .5 to 1dh, GH 7dh.  
> The results are after one day of adding baking soda in the amount of
> 1/4 tsp:
> pH 6.0, KH .5 to 1dh, GH .5 to 1dh.  I said GH .5 to 1dh.  

The lack of change in pH or KH is consistent with the very small
amount of baking soda you added.  The change would be within the error
margin for either measurement. 

> I retested all of the values because I was shocked to see the change
> in GH.  Did the GH figure drop this far down because my plants are
> extracting the need for CO2 ( carbon ) from my GH?  This is the
> decalcification process or something like that in action?  The fish
> are fine.

No, GH measures mostly calcium and magnesium, not carbon compounds.
It may be that plants are using the calcium and magnesium but the rate
seems pretty high for that.  Are you adding anything to the water that
would act as a chelator?  Peat in the filter?  

Biogenic decalcification is the result of plants extracting carbon 
from the carbonates causing calcium to percipitate on aquarium
surfaces.  This will actually raise the pH, even though it seems

> I have a 30 gallon plant ( if you can call it that ) :) tank with two sword
> plants in it.  They are very healthy.  I have had them for years. I added
> 1/4 tsp of baking soda to this 30 gallon tank yesterday and here are the
> test results from today.
> pH was 6.0, it is now at 6.6.  KH stayed the same .5 to 1dh.  GH stayed the
> same 7dh.  The pH went up so shouldn't I see a change in the KH?  

Again, perhaps the results are confused due to measurement error.
What kind of test kits do you have?  What is the resolution of the pH
and KH test kits?  If the pH test kit has a resolution of 0.4 and the
KH test kit has a resolution of 0.5, you have a wide range of possible

> Baking soda ( sodium bicarbonate ) raises the KH only?  


> Is KH part of the GH?

In generally accepted *hobbyist* terms, KH is the measure of HCO3- and
CO3--; GH is the measure of Ca++ and Mg++.  KH and GH are totally

However, typical hobbyist test kits seem to measure total *alkalinity*
or acid buffering and call the results "KH".  If carbonates are the
only buffer in your water, i.e., the only contributor to alkalinity,
this is OK.  If you have other buffers such as phosphates (from pH-UP
or -DOWN or other additives), the "KH" measurement is up for grabs.

Some test kits measure "total hardness" which is a combination of 
KH and GH.  This type of measurement is of little value to us. 

In general, I prefer the Tetra KH and GH test kits.  Our tap water is
relatively low in alkalinity and the values we measure with these
kits seem very "true". 

Just so I don't get flamed yet again by our chemistry professionals,
"KH" and "degrees" are scientifically undesireable terms.  But since
the test kit makers continue to use them, so will I.

> Calcium carbonate will raise the GH, but not the KH?

The calcium ions will raise GH and the carbonate ions will raise KH.