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Discussion Starter · #1 ·
Hi all,

So how does CO2 dosing work? Looking at the CO2/pH/KH chart, I see that you want 2 values to line up to one and I've heard bubbles aren't a good way to measure. How would one get to 20-25 ppm? What is the basic reference point? If anyone has the steps they used to calibrate their CO2, that would be a great help!

For example: I have an aquarium with 'supplemental' (not injected) CO2. My pH is 6.8. My KH is 3. So the chart says my CO2 is 14.3 ppm. I want it at 25 ppm. So do I raise KH, lower pH, or would you adjust the CO2 first?

Thanks!
 

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Discussion Starter · #3 ·
This supplement: Fluval Mini Pressurized CO2 Kit, CO2 Supplement for Planted Aquariums. So probably not much CO2 from this and likely not relevant to my question but I included the fact just in case. I'm not injecting CO2, but the question is for when I do in the future.
1025061
 

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That system is injecting CO2, it's just way more expensive in the long run.

To answer your question, the KH measurement of your tank will not influence the amount of CO2 in the water; it's used as a measurement point to calculate the CO2 (based on your ph). If you were to raise your KH without changing your injection rate, you would see a rise in your ph as well. You would stay at 14.3ppm. Instead, you need to increase your CO2 injection. This will cause your ph to be lower, with the same kh. With a KH of 3, you're going to want to shoot for a ph of 6.4-6.5.

Also to consider, is that you're trying to reach that ph by the time your lights come on, and holding it there throughout the day. Having a changing CO2 concentration during a single photo period is referred to as "fluctuating CO2", and can be just as bad as it being too low.

I recommend reading this article on 2hr aquarist. It's a little dense, but it's massive help in figuring out your CO2 injection goals.

Surface agitation in CO2 injected planted tanks - The 2Hr Aquarist
 

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As mentioned that is injected co2. It just won't last very long (unless your tank is tiny) and not very economical in the long run. If you want to keep it simple go by the PH change, know as the PH Drop. That's what most of us do here. Take some tank water and let it sit out over night and measure the ph in the morning. Then measure you PH drop when co2 is running for a while (for me that's the middle of the light cycle). Co2 lowers PH so your looking for roughly a 1.0 drop. The 1.0 drop generally equates to 30 or so PPM of co2. You should also get a drop checker if you don't have one for a quite visual whether the co2 is low, good or possibly too high.

BTW the chart is meaningless for many setups since their are many variables that can affect PH/KH (i.e. rocks) that will throw off the numbers.
 

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Discussion Starter · #6 ·
I get it now. Thanks for the warnings about fluctuating CO2 and relying too much on that chart! The CO2 I'm putting in now is expensive in the long run, so I have a few 5 lb CO2 tanks ready for the aquarium that I'm currently growing Monte Carlo in but I still need a few components for the system to work. That CO2 cartridge thing I'm just using for my plant holding tank for now - nothing serious. Much appreciated
 

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Sorry to piggy back on this, but it reminded me about a question I have. Short version is does injected CO2 add to the KH (Carbonate Hardness) of the water?

I have had CO2 running and have kept it at a steady flow that looks reasonable. I also had one of those CO2 checkers that has the bulb and fluid inside but recently misplaced the replacement fluid. I have not changed it since, it has been the same since both because I haven't touched the regulator and the bubble count is still the same. I am trying to work on my waters GH right now and while this was helpful with that and the relationship between GH and KH, I was curious if my CO2 is boosting the KH up?

Also unsolicited advice to lower GH without going R/O would be appreciated.
 
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