I have a heavily planted 180g tank that i have just added CO2 injection. Bubble rate is 3bps. My drop checker with standardised 4 degree KH is always blue. CO2 is linked via solenoid to lights. I have 24 hr gentle water rippling. Tap water KH is 2 but i initially added KH buffer so it is now 5. My pH meter shows 7 before lights on and 6.4 just before lights out.
My question is will softer water ie. KH 2 allow me to reach my desired 30ppm of CO2 quicker than say my current KH of 5? Otherwise i may have to crank up my CO2 even further. I have an Aquamedic 1000 external reactor powered by an external pump . I see lots of very small bubbles at the outlet that is at the bottom of the tank. Pump flow rate is 2000 litres/hour.
LAKA

The only way to get more CO2 into solution with the water is to add more to the water. Raise the bubble rate, wait a few hours, see if the drop checker is green yet. If it isn't repeat the above. The only thing KH does is change the pH of the tank water for a given ppm of dissolved CO2. How much it changes it depends a lot on what other stuff is in the water, such as your KH buffer.

I thought the lower the KH the more free CO2 is available in the water to dissolve in it whereas a higher KH means CO2 is then bound into the carbonate/bicarbonate system thus less is available for plant uptake.

Another way of viewing this is as follows. We have 2 identical tanks in every aspect except KH. One is KH of 1 the other is KH 10. Both tanks get same rate of CO2 infusion. Which tank (if any) will achieve 30ppm CO2 quicker?

LAKA

*Sigh*

Laka, I already replied to your thread on the APC forums. You are now shopping for the answer you want to hear. Fortunately, chemistry isn't going to change for you.

Like I said there and say here again. The only way to increase you ppm of CO2 is by adding more CO2. KH has nothing to do with it.

The reason why i am posting the same thread on this forum is because no one answered the question i have put forward. I am still waiting for an answer. Please read the question and answer it. I KNOW i can just open the needle valve to get more CO2. But if i can conserve CO2 and still get 30ppm at a lower KH is this not a smarter way of doing it?
LAKA

Well I thought that no matter what your kH, you are basically always driving your pH down by about 1.0... A quick look at a pH/kH chart for measuring CO2 confirms this. Your base water should measure ~3ppm of CO2 so with a kH of 2 your pH should be 7.3 before CO2 injection. From there you need to get to 6.3 for ~30ppm of CO2. At a kH of 5 your base pH should be 7.7 with a target of 6.7 to get your CO2 to 30ppm.

Any way you look at it, you are bringing your pH down -1.0. I don't think more or less kH will change that.

OK it appears the general or actually the unanimous consensus is Kh does not affect CO2 levels. I will reduce the Kh to 2 with water changes keeping CO2 constant and see what happens to the drop checker. Will keep you all posted.
LAKA

if you add CO2, the KH will raise a very very tiny bit. But this is not detectable with our testkits. So in practice, the KH will remain the same.

greets,

yme

To answer your question, yes. It requires less CO2 gas to be dissolved in water with a low KH to reach a certain ppm of available CO2, than with a high KH. So for your 2 tanks the one with the KH at 1 will achieve 30ppm CO2 before the one with a KH of 10 when the bubble rates are the same. It can be calculated using Henderson-Hasselbalch Equation. This is all very well in theory but in reality you'll be hard pushed to notice any difference with the KH levels we normally operate at.

Actually the chemistry of adding CO2 to water is quite interesting - if you're that way inclined

James

Thanks for the reply James C I always thought that to be the case but if the differences or going to be almost negligible at the KH levels we're working at then it probably wouldn't make that much difference.
HOWEVER dapellegrini makes a very interesting observation. If a pH level drop of 1 unit is equivalent to 30ppm CO2 increase then why use a drop checker at all??