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post #1 of 4 (permalink) Old 02-23-2016, 10:24 PM Thread Starter
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Question CO2 Question

I'm upgrading my CO2 system to a solenoid setup. How much CO2 should I inject on a daily basis? Should I rely on the drop checker and stop injecting when it reaches green?
The reason I'm asking this is because my old setup was a CO2 canister and my drop checker read yellow at all times. Just as an experiment until I connect the solenoid system I disconnected the canister and it has taken 16 hours+ for drop checker to reach slightly green.
I'm just trying to fine tune bubbles per second and the amount of time I should have CO2 running.
Thanks for any advice!
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post #2 of 4 (permalink) Old 02-23-2016, 10:46 PM
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In my opinion, it is not safe to relly on bubbles per second, nor can anyone recommend a number (hard to count for bigger aquariums, bubbles vary in size, aquarium size matters, light , plants, fish , surface movement, KH...)

A drop checker with 4dKH solution is better ( not with aquarium water). The major problem is that it has a display lag of 1-2h. The other problem is that it measures onyl localised CO2 levels.

KH- pH readings are a little better for fast response and can show if you are heading in the right direction and how fast.

How big is the aquarium ? What KH ?

Star slow and increase until fish are stressed or gaspinng. I aim for a light green at peak CO2.

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post #3 of 4 (permalink) Old 02-24-2016, 12:48 AM Thread Starter
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Thanks for the advice dukylaf.

I'm new to this so I am starting with a nano tank, 5 gallon and heavily planted(that's my focus) and a Red Crown Betta. The water parameters(PH, Nitrites and Nitrates) are great and the tank is cycled.

You are absolutely right about the lag. It took 18 hours for the drop checker to turn green so I would assume in my tank specifically, once the water is saturated with CO2 it takes in between 14-16 hours to come down to acceptable levels. I'm just wondering that now that I'm gonna have more control over the CO2 injection, should I just turn it off when it reaches saturation? I have a Betta so the CO2 wouldn't affect him but I want the CO2 injection to be as efficient as possible so I don't waste it.

I'm a newbie so I'm still studying about KH. How important is it?

Thanks again!
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post #4 of 4 (permalink) Old 02-24-2016, 01:30 AM
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Glad to help. Good choice with the Betta and CO2 ... gives you a little more wiggle room. Keep in mind for such a small aquarium you need very fine adjustments.

What I mean about the dropchecker lag is that if you reach optimal values (~30ppm CO2) at 12:00, your drop checker will turn the right green color for 30ppm at 1 or 2:00.

The lag you observed is independent of the measuring method. It takes time for the CO2 to build up to a certain concentration and it takes time for CO2 levels to drop down from a certain concentration. This is why most start adding CO2 an hour before the lights are turned on. This depends on the injection method, surface aggitation, surface to volume ratio, aquarium size etc. To give an example, if i take a cup of water from my aquarium and leave it in the room, it takes about 20h to get a stable pH of 7.5 (degassed pH). The water in my aquarium never goes over 7pH ( even with CO2 injection stopped, it is still there ). When I start adding CO2 the pH drops to ~6.4. I double check my pH measurements but even if they are off, the drop checker tells the same story, just with a 2h delay.

Once you reach your target CO2 you can turn it off. For how long that is a more complicated question ... The dropchecker will change colors too slow... but adjustments can be done over some days. Say you want lime green. Once the dropchecker reaches that point turn the CO2 off and record hour H1 (for Ex =12:00). When the dropchecker starts to be dark green record hour H2 (=16:00). Now to adjust your schedule ... turn off your CO2 at H1-2 (10:00), turn on at H2-1:30 (14:30)... and repeat until you have a consistent color from lights on to off. You can see why a pH measurements is more accurate and why most people do not bother turning it off and on during lights on period.

The most relevant thing for this discussion is that CO2 will lower the pH but not the KH. In theory, if you have a stable, known carbonate hardness (~KH) you can approximate the concentration of CO2 just by looking at the pH. So you will have a good/high CO2 (~40ppm) at pH 7 when KH is 12, but the same ppm CO2 will give you a pH of 6.4 at KH 3. Here is a detailed table about it

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