idea for a CO2 controller - The Planted Tank Forum
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post #1 of 23 (permalink) Old 01-31-2010, 05:44 PM Thread Starter
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idea for a CO2 controller

I was doodling in my sketchbook and came up with this.

The CO2 level is control by microcontroller that has a ph probe in 4dkh water. It's basically a giant drop checker.

Since, it's so big it has to be inline with the filter, under your stand. I can see it being filled up with regular tank water if for some reason the output of the filter is blocked off or maybe when the filter is off?

So the assembly has to be easily disassembled for maintenance.

Hey, no more worrying about bubbles/second or the color of the drop checker liquid.
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post #2 of 23 (permalink) Old 01-31-2010, 06:14 PM
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What would be the advantage over just dipping the probe in regular tank water (filter outflow or not)?

Initially it would need to be dialed in, but with the kH being fairly constant, after that it should result in the same controller function?


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post #3 of 23 (permalink) Old 01-31-2010, 06:21 PM Thread Starter
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if tank water KH is constant then this setup is not needed
good point.

By writing a good piece of software for the MC, it can figure out the CO2 levels for any fixed KH.

so this will work fine?
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post #4 of 23 (permalink) Old 01-31-2010, 06:34 PM
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Kinda costly you can get them cheaper - $110 shipped plus when I bought mine I got two probes. Not sure if they messed up or they do that all the time but I didnt complain.
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post #5 of 23 (permalink) Old 01-31-2010, 06:42 PM Thread Starter
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I found the formula for finding CO2.

CO2 (in PPM) = 3 * KH * 10^( 7-pH )

I have a microcontroller sitting around doing nothing so I might do something with it


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post #6 of 23 (permalink) Old 01-31-2010, 06:44 PM
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mistergreen in your first picture what would stop the tank water from getting inside the 4dkh?
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post #7 of 23 (permalink) Old 01-31-2010, 06:45 PM
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It won't work. The reason is the very slow response of the drop checker to CO2 ppm changes. This would result in overshooting on CO2 to the extent of killing fish, then undershooting by so much as to trigger algae blooms. It is possible to make a drop checker with a gas permeable membrane separating the 4dKH water from the tank water, with a very tiny pH probe to measure the pH of the 4 dKH water. This greatly improves the response time of the drop checker. But, it is very difficult to make such a drop checker and keep it working, so the effort far exceeds the benefits.

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post #8 of 23 (permalink) Old 01-31-2010, 06:47 PM
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Quote:
Originally Posted by mistergreen View Post
I found the formula for finding CO2.

CO2 (in PPM) = 3 * KH * 10^( 7-pH )

I have a microcontroller sitting around doing nothing so I might do something with it
That equation works for water that contains only carbonates and CO2 that affect the pH, but it doesn't work if there is anything else in the water that affects the pH. That's why a drop checker works, and why just measuring the tank water KH and pH doesn't work.

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post #9 of 23 (permalink) Old 01-31-2010, 06:51 PM Thread Starter
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Quote:
Originally Posted by StillLearning View Post
mistergreen in your first picture what would stop the tank water from getting inside the 4dkh?
Not sure, air pressure?


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Originally Posted by Hoppy View Post
It won't work. The reason is the very slow response of the drop checker to CO2 ppm changes. This would result in overshooting on CO2 to the extent of killing fish, then undershooting by so much as to trigger algae blooms. It is possible to make a drop checker with a gas permeable membrane separating the 4dKH water from the tank water, with a very tiny pH probe to measure the pH of the 4 dKH water. This greatly improves the response time of the drop checker. But, it is very difficult to make such a drop checker and keep it working, so the effort far exceeds the benefits.
Good point about the delay.. Would it apply if the probe was directly in the tank probing the ph of the water column?


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post #10 of 23 (permalink) Old 01-31-2010, 06:54 PM Thread Starter
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Quote:
Originally Posted by Hoppy View Post
That equation works for water that contains only carbonates and CO2 that affect the pH, but it doesn't work if there is anything else in the water that affects the pH. That's why a drop checker works, and why just measuring the tank water KH and pH doesn't work.
ah, so probing the pH in the 4dkh solution is a more accurate but it would obviously has other issues.


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post #11 of 23 (permalink) Old 01-31-2010, 06:56 PM
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I'm not sure I would think some kinda water would still get in unless you get a gas permeable membrane like Hoppy was saying. I use a sms122 with a drop check as backup and never had a problem yet.
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post #12 of 23 (permalink) Old 01-31-2010, 07:02 PM Thread Starter
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i hear those fish breather bags make good gas permeable membranes.

StillLearning: it works for you but not necessarily somebody else with something like well water or some other situation like a lot of tannic acid from driftwood. It might blow up the whole setup.


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post #13 of 23 (permalink) Old 01-31-2010, 07:07 PM
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StillLearning: it works for you but not necessarily somebody else with something like well water or some other situation like a lot of tannic acid from driftwood. It might blow up the whole setup.
Thats why I have a drop check in the tank as well so I can check my readings and make adjustments.
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post #14 of 23 (permalink) Old 01-31-2010, 07:13 PM Thread Starter
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Originally Posted by StillLearning View Post
Thats why I have a drop check in the tank as well so I can check my readings and make adjustments.
do you have your sms122 controlling a solenoid?


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post #15 of 23 (permalink) Old 01-31-2010, 07:15 PM
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Quote:
Originally Posted by Hoppy View Post
It won't work. The reason is the very slow response of the drop checker to CO2 ppm changes. This would result in overshooting on CO2 to the extent of killing fish, then undershooting by so much as to trigger algae blooms. It is possible to make a drop checker with a gas permeable membrane separating the 4dKH water from the tank water, with a very tiny pH probe to measure the pH of the 4 dKH water. This greatly improves the response time of the drop checker. But, it is very difficult to make such a drop checker and keep it working, so the effort far exceeds the benefits.
How much time and money did you invest in the LED system and what was the cost/benefit vs a T5ho diy system?
Some times a project is worth doing for the learning experience, (I know Hoppy subcribes to that). The basic concept outlined is how CO2 probes function any way. They are not based on micro probes but they do employ a permeable membrane. I agree with the lag time arguement - that is something you should consider in your design.

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