CO2, pH, and baking soda

C

cowman345

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Oct 10, 2005
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I've searched and searched and read and read, but am still left making some assumptions that I need clarified, please:

I realize that to acheive proper CO2 injection rate, I must determine the desired pH and KH for my tank.

If I have a bunch of cichlid sand mixed in with caribsea's ecocomplete plant substrate, I assume this will stabilize my KH (right?).

So, I'm guessing I have to adjust pH without affecting KH... does baking soda do that? Am I on the right track here?

-dave-
 
I read somewhere that alot of tanks with Co2 crash after a year or two.
You should look into this
acid<-------Ph-------->alkaline

Kh is carbonate hardness
baking soda is mostly sodium
a ph on the slightly alkaline side is good for living things
a side effect of baking soda is that it raises ph or Kh
Now I don't know how accurate this info is but it seems to be as far as iv'r gotten on the subject & may have worded it wrong but may clear up some stuff allowing you a to go onto a deeper understanding on your own. Some of this stuff I can read over a few times b4 it makes sense.
Maybe someone can clairify what the difference is between kH & pH as far as I can tell carbonate hardness is the units(measurement ) & pH is the scale.
A low ph meaning it is acidic(or soft) & an alkaline ph meaning it's hard
What I REALY want to know is if heavy water is hard, like the type of water used to cool can-du reactors. ANY1 KNOW? or can anyone correct anything iv'e said here for cowman?Maybe it's hard water & not heavy they use to cool rods in powerplants
 
Last edited:
Here is what I understand about the relationship between KH & PH, please correct me if I'm wrong.
KH is the measure of dissolved calcium in your water.
pH is the scale that measuers how alkaline, or acidic your water is.
KH acts as a ph buffer. The higher the KH the harder it is to bring down your pH.
 
Dave, the 'desired' CO2 rate is 25 - 30ppm. The kH/pH relationship tells you what your CO2ppm is.
Take a sample of tap water, set it out on the counter for a couple of hours. Then test for kH(at this time it would be advantageous to test for gH, ph and nitrates as well) to determine how much 'buffer' your source water is giving you.
If you have a kH of 3°-5°H from your tap you need do nothing to change it to safely inject. The kH (carbonate hardness) of your water is what keeps your water's pH from 'crashing' when using gas. Having 3°H(4° is better) or higher means that you need add nothing further to buffer up your water.
Some people mistakenly believe that if they adjust their pH down, they are increasing their CO2 ppm. In reality, the only way to increase CO2 ppm is to increase flow rate of the gas into the tank.
This is the way I set it up when beginning to inject. Make sure you have 3°kH, minimum. If you do, stick the end of the tubing from the CO2 source into the tank water and set the bubble rate at one bubble every 3 seconds.
When you have it set, insert the tube into your reactor and wait 2 hrs. and test the pH to determine content. Make small adjustments in flow to achieve 20ppm/CO2. Check this measurement every two hrs. all day and again in the morning at lights on. The pH will drop slightly in the dark hrs.
When you find that you have no more than 30ppm at lights on, over period of days to a week, you have your desired flow rate.

Len
 
Clarification:

KH = Carbonate and bicarbonate in the water, aka alkalinity. It is a measure of the water's natural buffering. It is responsible for both the pH and the resistance to change of the pH.

GH = "Hardness" or the calcium & magnesium content of the water. It has nothing to do with pH.

CO2 injection has nothing to do with tanks "crashing" over time.

Sodium bicarbonate = NaHCO3. Sodium at.wt. ~23, H at. wt. 1, C at.wt.~12, O at.wt ~16 (x3 = ~48), therefore sodium at 23/84 = ~27% of sodium bicarbonate, while the bicarbonate at 61/84 = ~73% of sodium bicarbonate. There are many folks on the web who do not know things, and that is not a problem in itself - the web is great place to learn. Many of those folks however are perfectly willing to post incorrect information and mislead others on topics they know absolutely nothing about.

I agree w/Len's comments.
 
Thank you all for your help,

RTR and Len - I really appreciate your clarification. It seems I understand this more than I thought, now I have a firm grasp.

One quick question: Len reccomended testing my tap water first. When testing my water, since I intend on having cichlid sand in my tank, I plan on making my initial water tests after the tap water has sat in the tank with that substrate for awhile since this will invariably alter the KH. Does this sound about right?

-dave-
 
You should also do a test of water from the tap that has outgassed that is not in the tank. This way you have an idea of what the substrate is doing to your water if anything.
 
Yup, agree w/that also. But after some time in the tank the substrate effect will be reduced by coating with biofilms (mainly slower response), somewhat offset by the fact that substrates tend to be more acid than the water column above them.
 
Test what ever you want, but you should know the basics of your source water. This is important for the long term. Your tank water will be affected, for the most part, in the short term.

Len
 
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