Can't Get Co2 Levels High Enough In 225 Gallon Tank With Overflows And Sump.

Lou Ahlquist

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Oct 7, 2018
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Central NJ
I have a 250 gallon reef type set up with overflows going into a sump. The sump and tank are completely covered, though not air tight. I've had this tank from my reefing days. The problem is I can't get a pH drop greater than pH= 0.9 and rarely a 1.0 pH drop. I suspect that the overflows could be part of the problem since it introduces a lot of gas exchange into the system (lots of water turbulence in them). I would ultimately like to get at least a 1.2-1.5 drop... I would like to be able to go as far as I need to in order to increase my light energy to ~120 PAR over the tank.

There is inherently so much dissolved O2 produced by reef tanks (overflows/sump) that the CO2 could probably be pushed quite high without damage to the fish furthermore, I am sure that ultimately Decreasing what causes the O2 to rise so high would in turn automatically Increase the CO2 level by preventing less gas exchange.

I have an AquaMedic 1000 CO2 reactor powered by a Sicce 2.0 pump which is what is what is required for this reactor. I push through 100 cc/min CO2 through the reactor. The CO2 obviously never shuts off all day.
The Aqua medic 1000 was the largest reactor I could find.

The tank does ok at this CO2 level when I am running about 80 PAR at the substrate and has been for about 1.5 years. It's when I raised the PAR level to ~120 PAR that I became aware that there just isn't enough CO2 to compensate for the increased metabolic demand of the plants at this energy level! Green algae is now covering most of the plants leaves and sides of the tank. I have to clean the front glass every day. Last night I shut off the extra 2 - T5 tubes and went back to my old light level. I am pretty sure it's from not enough CO2.

I would appreciate any thoughts or solutions regarding how I could increase my CO2 level.
I am scratching my head at this point.
 

Darren Blann

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Nov 2, 2020
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Uk
I'm having the same issue. I'm running a sump, my CO2 is on point but I am using eco complete, so it's the only thing I can think of that is causing green dust on the glass and plants as the plants can't thrive in eco complete when using CO2 and high light. Good gaseous exchange is a benefit, but as you say can use more CO2, but I think that is what sump users like us may need to put up with lol. A inline CO2 defuser will help dissolve CO2 and distribute it better, I will never go back now unless it's a small tank.
I'm about to shut my tank down and start again with tropica soil.
 

Chris Noto

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Feb 27, 2008
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Atlanta, Georgia, USA
I don’t see enough information on either of your systems to diagnose the problems that you describe. What are your water parameters, starting and before a water change? What are your animal stocking levels? What are your water change programs, and how consistent are you with that?

Accurate diagnosis depends on adequate information. A headache could be from tension, or from a tumor. No way to tell without data.

To me, blaming a substrate, and tearing down the system to replace it, without a thorough analysis of the system is like doing brain surgery for a headache without a scan and other indicated tests.

Of course, as always, YMMV. You bet your money and you take your chances.
 

easternlethal

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Dec 26, 2014
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Hong Kong
I have a similar setup with same size tank, sump, overflow etc. I wouldn't get to obsessed about ph drops as long as plants, fish etc. are healthy.

But if really want to crank up CO2, just put your CO2 outflow into the inflow of your sump's pump and ditch the reactor. You'll then be able to push through as much CO2 as you want.

If you really like a reactor then you'll need to build a bigger one (they are easy to make).

It's true you'll need more compared to a canister setup but the benefits of a sump makes it all worth a lil extra CO2 imo.
 

Zeus

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Oct 20, 2016
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I would appreciate any thoughts or solutions regarding how I could increase my CO2 level.

Twin CO2 injection/reactors !!, I have a 500l with Twin CO2 injection/reactors and have no problem dropping the pH over 1.0 in less than 30mins. One of our members at UKaps has a 2,000L High tech BEAST with sump and overflow and he has no issues (uses lots of CO2). The answer my be in his journal

heres my injection rate


We also have some data on the CO2 used per tank size which may help also
 

Jellopuddinpop

New Member
Jan 10, 2021
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CT, USA
On my tank, I built a three stage Cerges reactor to make sure I never ran into CO2 problems. This is what I would suggest...

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