Choosing a DIY CO2 Absorber to Build
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Old 05-14-2014, 04:41 AM   #1
KhanQueso
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Choosing a DIY CO2 Absorber to Build


I am looking at making a DIY CO2 Absorber, and I am considering two different options.

The first is spin off of the traditional Rex Grigg or Cerges style reactors where CO2 is trying to rise against downward flowing water. The twist here is that I would make the body "conic" instead of cylindrical. Since water velocity is a function of flow rate and cross-sectional area, I can get CO2 bubbles to "hover" in the water column by expanding the the cross-section. (Hopefully) no air pockets to create noise at the top or bubbles blown out the bottom.

The main challenge with this design is narrowing the top down enough to make sure that bubbles cannot reach it and form a gas pocket.

An example of the "conic" reactor. Not really conic due to difficulty in construction, but will function nearly identically. Water in the top, out the bottom. CO2 will be introduced upstream of absorber and flow into it with the water.


The second is a more technically intricate design that tickles my inner engineer. The only mention I have seen of this design in aquaria is by Rezco, who has mentioned it here. Essentially, we capitalize on the bubble that forms at the top of the reactor by spraying water onto packing with a large surface area (macroscopic, not ceramic pellets). Since absorption primarily occurs at boundaries between CO2 and water, this method will ensure highly effective CO2 absorption.

The issue I have is that the CO2 absorption is not readily controllable except by changing water flow-rate with an array of pumps or motor controller (both are pricey). Another issue may be algae or other bio-growth clogging the packing, I have seen this issue in person while working on similar equipment used to scrub chemicals from exhaust gas.

Ultimately, either design will probably be overkill for my 40B.

Has anyone made either of these before and wants to chime in with experiences or advice? I like to look before I leap.
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Old 05-14-2014, 12:56 PM   #2
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i like the cone idea but space under a tank be the big issue i see, the idea is right force the pocket of air back down again and again.
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Old 05-14-2014, 05:24 PM   #3
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Space won't be too bad for me. I (accidently) created the perfect cubby hole in my aquarium stand to throw this in.

For either method I will need a pump to increase/control flow rate. I don't want to restrict canister flow to control the absorption of CO2 in the second design and it simply doesn't have enough flow rate to work with the cone absorber.
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Old 05-17-2014, 04:27 AM   #4
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Bad news:

I attempted, and failed, to construct the "conic" absorber. I snapped the plexiglass in two right through the middle of one of the sides

I was thinking on doing an instructional thread on it if I got it to work, but I apparently need instruction myself

Good news (everyone):

After talking to my boss during lunch today, he and I have come up with another design that I might try.

The CO2 absorber is a tightly wound helix of flexible tubing that is slightly over-sized from the rest of the plumbing. Essentially, the absorber forces the water to stay in contact with the CO2 for a long time by increasing the distance the water and CO2 have to go before reaching the tank. The larger diameter of the tubing also slows the water velocity down, further increasing the time they remain in contact.

Here is a diagram:


The increased length of piping will increase head loss, so a booster pump needs to be added. By using a larger than necessary booster pump and adding a throttle valve after the CO2 absorber, we can also raise pressure in the CO2 absorber slightly while controlling flow rate. This will aid CO2 absorption, though perhaps only marginally.

The major con to this is the additional cost of an external pump, but it should (hopefully) be an effective design.

Thoughts? Opinions?
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Old 05-17-2014, 08:26 PM   #5
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Have you figured a way to get the filter reprimed after cleaning? I think this may be reinventing the wheel? Or is it just an interesting thought to keep the brain active?
I wonder about the value of adding a second pump to the system. Doesn't the cost of the second pump and valve throw it out of the "effective" category?
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Old 05-17-2014, 09:36 PM   #6
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Quote:
Originally Posted by PlantedRich
Have you figured a way to get the filter reprimed after cleaning? I think this may be reinventing the wheel? Or is it just an interesting thought to keep the brain active?
I wonder about the value of adding a second pump to the system. Doesn't the cost of the second pump and valve throw it out of the "effective" category?
In my experience, my canister can prime itself after reconnecting. If necessary, I can add a drain before the coil to help pull water through the canister to prime it.

Also, the diagram does not reflect all components of the system. The quick disconnects on my filter are not shown. When the filter is serviced the rest of the plumbing will still be filled with water. I could even add a bypass around the filter to allow the CO2 dosing to continue when it is disconnected.

By "effective" I meant "dissolves CO2 without flushing bubbles into the tank or developing noisy air pockets". Ultimately, adding a second pump does reduce cost-effectiveness significantly (which is definitely a major concern). I won't deny it, this design is not particularly cost-effective for me. However, the pump may be unnecessary for aquariums that already have an over-sized circulation pump in place, such as the return from a sump filter.

I am looking into lesser-explored areas of CO2 absorption in this hobby for a couple reasons. Mostly, I enjoy the problem solving process and it helps to keep my brain active (my internship doesn't seem to be cutting it for me). I also hope to find an alternative design that others may find useful. If I have to reinvent the wheel 10 times over in order to find a better version, so be it!

Last edited by KhanQueso; 05-17-2014 at 09:42 PM.. Reason: Forgot to say something
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Old 05-17-2014, 10:53 PM   #7
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The "conical" chamber idea should work fine, but you would want to make it a pyramid shape, and use 1/4" thick acrylic. It isn't hard to make an effective CO2 diffuser/reactor/absorber for most tank sizes, but if you have a 100 gallon or larger tank, an idea like this may be worth pursuing. But, don't complicate it with added pumps. The output from a canister filter is at a low enough pressure that there would be no risk of rupturing the pyramid, but add an auxiliary pump, that produces a pressurized flow, and all bets are off.
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Old 05-18-2014, 01:57 AM   #8
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Thankfully, I never intended to use the "conical" chamber method with a pump, just my canister filter.

Unfortunately, all attempts at making the chamber have failed. I am trying to score and snap because I lack the proper tools to get a nice straight cut any other way (one of the detriments to being at college).

I spent half an hour scoring a piece of plexiglass this morning (trying to make a smaller chamber with the scraps from my first attempt). It still fractured incorrectly when I tried to snap it.

I also went to my hardware store to see how flexible their plastic tubing is... only to be met by disappointment. The helical design would be impractically large using tubing over 1/2" internal diameter. If only copper was aquarium safe...
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Old 05-18-2014, 03:46 AM   #9
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I "cut" acrylic by scoring it several times with a utility knife, sometimes on both sides, then clamping the smallest piece between two boards. Then you can usually snap it without cracking it.
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Old 05-18-2014, 05:34 AM   #10
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Quote:
Originally Posted by Hoppy
I "cut" acrylic by scoring it several times with a utility knife, sometimes on both sides, then clamping the smallest piece between two boards. Then you can usually snap it without cracking it.
That is almost exactly how I tried to do it. Maybe my pocket knife was not cutting well enough... how deep were your scores just before snapping? I just measured mine to be around 1/32 in on both sides.

Seeing that the score and snap method does work for acrylic is heartening. Now I just need to figure out what I'm doing wrong.
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Old 05-18-2014, 04:27 PM   #11
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I never know how deep my score marks are. I use a pretty new utility knife blade, a straight edge, and score it up to 5-6 times. The only times it hasn't worked is when the short piece is too short - less than about 1/2 inch. Then the short piece tends to break off at a diagonal, leaving a much too short piece to ever break off. I have only used this on 1/8" thick or thinner acrylic and lexan. I'm sure 1/4" thick acrylic would be harder to break, but I just saw if off at that thickness, with a hacksaw or jigsaw.
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Old 05-18-2014, 07:02 PM   #12
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Quote:
Originally Posted by KhanQueso View Post
I spent half an hour scoring a piece of plexiglass this morning (trying to make a smaller chamber with the scraps from my first attempt). It still fractured incorrectly when I tried to snap it.
Buy the knife made for scoring acrylic sheets. It'll shave bits out needed for snapping. A knife usually is not the right tool. It'll score but not like the acrylic knife.
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Old 05-18-2014, 07:07 PM   #13
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So you don't score 1/4 inch acrylic? I guess that means I wasn't scoring it wrong, just using the wrong method. If I get a jigsaw I can probably get a straight line using the same straightedge I used to score it. I've already spent more money on this than I should have, need to wait for a paycheck or two to buy a jigsaw.

Thanks for the assistance on acrylic cutting.

In the meantime, my friend has given me a small water-cooler jug for this project, need to figure out what kind of contraption I can make with it.
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Old 05-18-2014, 07:51 PM   #14
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Quote:
Originally Posted by mistergreen View Post
Buy the knife made for scoring acrylic sheets. It'll shave bits out needed for snapping. A knife usually is not the right tool. It'll score but not like the acrylic knife.
But, with a utility knife, an adjustable wrench, locking pliers, and a roll of duct tape you can fix anything
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Old 05-18-2014, 08:36 PM   #15
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Quote:
Buy the knife made for scoring acrylic sheets. It'll shave bits out needed for snapping. A knife usually is not the right tool. It'll score but not like the acrylic knife.
I wasn't aware they made a special knife for this application. I'll have to check next time I'm at the hardware store.

Quote:
But, with a utility knife, an adjustable wrench, locking pliers, and a roll of duct tape you can fix anything
Don't forget WD-40! haha
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