Obsessing over CO2 - The Planted Tank Forum
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post #1 of 12 (permalink) Old 10-30-2015, 05:59 PM Thread Starter
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Obsessing over CO2

I am planning a large tank after about 15 years away from the hobby.

My previous large planted tank failed to prosper due to my cheapness and crappy DIY skills. I am in a different financial position now so I can afford a high tech tank, but I still am uncertain how get the CO2 out of the gas bottle and into the water.

This time around I have a dual stage regulator, quality needle valve, pH probe and solenoid. My tank will have a sump and I have been looking at the Cerges reactor which I intended to plumb into the sump. I even bought a 20 inch water filter housing. But I have just spent three hours reading that massive Cerges thread, and I am having second thoughts.

Here is a diagram of the sump I intend to place in the system:



Section B is mechanical filtration, section C is immersed biological media and section D is my auxiliary chamber.

I had intended to plumb the Cerges reactor into compartment D. But after reading that terrifying Cerges thread I considered my mechanical filtration chamber. It will be packed tightly with sponges and filter floss and should have a heavy flow of water through it. The water will be about 12 to 18 inches deep here.

Is there any reason why I shouldn't simply place the end of the CO2 line at the bottom of compartment B? Would not the CO2 be trapped by the filter media and completely dissolved? I realise there will be some out gassing. I could minimize that by getting rid of my auxiliary chamber and maybe the bubble trap.

Is there any reason why this wouldn't work, or why it would be a bad idea?

Any comments would be appreciated.
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post #2 of 12 (permalink) Old 10-30-2015, 06:14 PM
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CO2 dissolves into water easily but that also means it leaves water easily as well. The more water surface and agitation, the faster. So a sump can be a problem but I've read if you cover the sump it reduces degassing.


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post #3 of 12 (permalink) Old 10-30-2015, 06:32 PM
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I have a very similar set up to yours. But no two tanks are the same and you will have to play around a little to find your sweet spot. Ideally you want 100% CO2 diffusion in the Cerges reactor.

My first setup was plumbing the Cerges reactor in line with the return pump with the water flowing in the "right" direction as marked on the water filter. This hardly gave me and pH drops over few hours.

After numerous trial and errors, my final set up is as follows: I have a Rio 1100 pump in chamber F that feeds the Cerges. (This is independent of the return pump) CO2 is introduced via a venturi (comes with the Rio). Output is fed into chamber D. I played around with placing the output in different chambers but saw no significant change. I also plumbed the Cerges in reverse and added several sponge filters in it. I now get a 1.0 pH drop in 60-75 mins. I also minimized turbulence in the sump drain by using a "reverse" durso. This helped too.
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post #4 of 12 (permalink) Old 10-30-2015, 07:58 PM Thread Starter
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I understand I will loose some of the co2. I can take steps to minimise turbulence in the sump.

It just seems to me that my life would be easier if I didn't have to fiddle around with another piece of equipment. From reading that Cerges thread it seems that there are a lots of ways to screw up a co2 reactor. And the commercial ones that I have seen seem to assume an in-line configuration.

For me major considerations for getting a sump is to minimise clutter in and around the tank, and to avoid as much as humanly possible a disastrous flooding event.

If I loose 50% of the co2 through out gassing, I'll just fill up my co2 tank more frequently. If I loose 90% of the co2 obviously I have to rethink my low tech solution.

Bump: PPP, by "reverse Dorso" do you mean that the sump chambers were connected via bulk heads and stand pipes?
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post #5 of 12 (permalink) Old 10-30-2015, 08:20 PM
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No. Instead of water just draining into the sump, you 'T' of the drain to introduce a vent. Can send you a pic later.

How are you draining into the sump?
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post #6 of 12 (permalink) Old 10-31-2015, 03:30 AM Thread Starter
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The tank isn't built yet so the only pictures are the ones in my head. I intended to have two drains into the sump, one of which would be a full siphon throttled with a ball valve and the other a dorso drain pipe. I think it is called the herbie method in the US.

The drains will enter the sump via compartment A and terminate under water. Compartment A will overflow into compartment B for mechanical filtration.

I wanted the sump to be reasonably quiet which would mean I would try to reduce splashing and turbulence as much as possible. Out gassing probably won't be too much of an issue and CO2 refills are unlikely to be a significant burden on my time or finances (compared to the rest of the tank).

Ease of maintenance is one of my goals and if I can get rid of the CO2 reactor and get reasonable amount of the CO2 into the water I would be satisfied.

I will need to do some testing when the tank is built, but I foresee two potential problems:

1. The CO2 simply exists compartment B without being dissolved.
2. The CO2 forms a pocket under the filter floss and continues to be dissolved into the water after the solenoid switches the CO2 off.
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post #7 of 12 (permalink) Old 10-31-2015, 12:45 PM
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The natural position would be part of "The CO2 forms a pocket under the filter floss and continues to be dissolved into the water after the solenoid switches the CO2 off". I cannot predict how big a part but it shall be substantial as most of the water-flow will tend to go round the bubble. It would be much better if you use a simple Rex Grigg type in-line reactor on the return path of your aquarium.
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post #8 of 12 (permalink) Old 10-31-2015, 01:38 PM
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I have never run a sump but I did have a cerges reactor for a while until I built a Rex grigg reactor. Imo the Rex grigg works much better than the cerges and I'll never go back

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post #9 of 12 (permalink) Old 10-31-2015, 06:27 PM
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Each of the sump dividers that has water going over is a spot for degassing but smooth flow, less drop and covering the sump should help as the CO2 is heavier than air and would stick around. I'd lose the dividers between D and E. The area where the pump is is where evaporation takes place and the more water in there the better, nagging sump pumps are annoying. If I felt the need to have more mechanical filtration than the prefilter sponges I use I'd use socks and lose the separate compartment. My sump is currently one compartment with 5" of poret foam separating the drain from pump areas. Pumps and overflow tubes have prefilter sponges that are rinsed out weekly. I do have plans for dividers in a glass sump but it is sure taking time to get it going!

Herbie good, Beananimal better, have you come across that variation yet?

My first reactor was a short 12" Grigg reactor and it worked about as well as simply sticking the CO2 line in the pump's intake with slightly fewer bubbles and was difficult for me to anchor so it was out of the way. Of course it was always far too small for my 100-180 gallon tanks! Currently and probably permanently I have a 20" Cerges run on its own rio 2500 to its own return to the tank so I don't lose flow. It is assembled according to the instructions and works perfectly but I could easily put a ball valve to drop the flow if bubbles were an issue. Planted tanks do better with more flow to distribute nutrients, keep debris moving into the filter, I wouldn't want to waste energy by making a loop back into the sump.

I don't know why so many people have trouble with reactors. I follow the instructions and both have worked just fine. The inner tube in the cerges fits on the outside ring so it is larger diameter than if it was on the inside but it is just pressure fitted. I see large bubbles going about half way down the 20" housing and a few tiny bubbles coming out the return and pH drops 1 full point in about an hour with +10bps counting through the clear housing. The cerges' return sits between and is parallel to the split main pump returns
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post #10 of 12 (permalink) Old 11-01-2015, 01:13 AM
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Tom barr says with a sump your water is more oxygenated, allowing you to run a higher ppm of co2

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post #11 of 12 (permalink) Old 11-01-2015, 03:07 AM
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I run an 80G tank with a sump and a Cerges reactor and it works fine. For the sump I would suggest and HMF style sump and just put a few sheets or Poret foam in there instead of worrying about baffles. Super easy and effective, I prefer it over all the other styles of sumps I've had (overflows and wet drys). As for as the reactor goes, drive your CO2 reactor using a separate pump other than the return pump. I use one of the RIO pumps with a needle wheel and feel the CO2 directly into the venturi inlet on the needle wheel pump.

For the overflow, definitely take the time to learn and build the beananimal. It's so redundant that you will never flood and can be tuned to be pretty quiet.
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post #12 of 12 (permalink) Old 11-02-2015, 07:17 PM Thread Starter
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Quote:
Originally Posted by essabee View Post
The natural position would be part of "The CO2 forms a pocket under the filter floss and continues to be dissolved into the water after the solenoid switches the CO2 off". I cannot predict how big a part but it shall be substantial as most of the water-flow will tend to go round the bubble. It would be much better if you use a simple Rex Grigg type in-line reactor on the return path of your aquarium.
Yes, this would be a problem. I intend to automate the CO2 injection with a pH probe and solenoid valve. Such automation would be pointless if switching off the CO2 didn't stop CO2 dissolving into the water.


Quote:
Originally Posted by Kathyy View Post
Each of the sump dividers that has water going over is a spot for degassing but smooth flow, less drop and covering the sump should help as the CO2 is heavier than air and would stick around. I'd lose the dividers between D and E. The area where the pump is is where evaporation takes place and the more water in there the better...
I think this is a good idea. As I considered the sump layout I questioned whether I really needed to separate the equipment and the sump pump. I also questioned whether I needed a bubble trap in a fresh water aquarium. I can see a need in a salt water tank where foaming would be an issue, but I don't think this would be an issue in fresh water.


Quote:
Originally Posted by Kathyy View Post
I don't know why so many people have trouble with reactors. I follow the instructions and both have worked just fine.
I think this is one of those times when the question is the answer. From my reading and obsessing over the CO2 reactor, I understand there are a couple of important variables:

1. The height of the reactor
2. The flow rate of water through the reactor
3. The water pressure in the reactor

I think it may be the case that people who fail fail on points 2 and 3.

Point 2 should be self evident (a higher flow rate pushes more water past each CO2 bubble). However, I think point 3 is the more interesting one.

A lot of posters talked about the importance of head pressure, and it seems the classic design calls for the CO2 reactor to be plumbed into the return line to the aquarium. This would have the effect of pressurizing the reactor chamber.

In accordance with Henry's law the solubility of gas in a solvent is proportional to pressure. See:http://chemwiki.ucdavis.edu/Physical...ility_of_Gases. So it seems that a low powered pump simply returning the reactor water back to the sump might not be effective in dissolving the CO2.

With this in mind I have decided to persevere with the Cerges reactor. I intend to install a high pressure pump with a variable flow rate, and install gate valves before and after the reactor. This way I should have good control over the flow rate through the reactor and the pressure in the reactor.

Thanks to everyone for their help.

Last edited by user38; 11-02-2015 at 08:06 PM. Reason: Because I am anal compulsive
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