Ineffective CO2 scrubber - airflow too low?

[Dkmoo]

Hi All,

The picture shows the setup. Pretty basic recirculating set up with the BrS scrubber "out" end connected to the skimmers venturi and a drilled hole on the top of the collecting cup connected to the "in" end.

It's been running over a week now with no noticeable change to PH, and the media did not change color at all. I'm pretty sure I have a high CO2 problem bc my ph never break above 8 even tho my alk is close to 11 so I know there's co2 to be scrubbed. The fact that I see no color change suggest that its not scrubbing effectively

Any ideas why its not working? My current theory is that my skimmer is pretty small - reef octopus bh50 with the pump rated for 33gph water and 4.5scfh air max. So either not enough air, or too fast water (or both) is causing not enough air exchange.

For those of you with an effective scrubber how big is your skimmer's air and flow rate? I might DYI a secondary air reaction chamber to increase air exchange if it turns out my current skimmer is not enough.

Anything else you can think of that might be a cause?

 

[Randy Holmes-Farley Verified Community Expert]

Anything else you can think of that might be a cause?

How effective is a scrubber or fresh air to a skimmer depends on many things, including how much the tank is otherwise aerated with high CO2 air compared to the skimmer. The tank top, for example, is sucking in CO2 while the skimmer is trying to remove it. Overflows and such may also be aerating with high CO2 air.

 

[Brett S]

There’s an easy test you can try to see to identify if high CO2 is in issue. Take a cup of tank water and test the pH, then use a small air pump and an air stone to bubble air through the cup in the water for about 30 minutes next to your tank. Then test the pH again. If the pH goes up then you need more air exchange on your tank.

If the pH doesn’t go up, then take your cup of water and air pump outside and bubble outside air through the cup for another 30 minutes. If the pH goes up now then there is a high CO2 issue. If the pH doesn’t go up then it’s another problem.

 

[Dr. Jim]

I think that the fact that the OP said the media hasn't changed color may be a suggestion that there is a leak somewhere in the canister and/or scrubbing system. I've been experiencing the same problem. First, I had two canisters in series where I bored out the intake and outlets so I could insert, glue and seal larger tubing. After months, my media did not change color so I assumed there was a leak. I then bought two new canisters with 3/4" threads thinking that my DIY was leaking. But I found the same thing. After a month, very little color change. I even applied silicone to the top of the gasket of the cartridge to assure there is no leak there. (Another possible area of leakage could be from not tightening the canister threads tightly enough....something that is very difficult to determine with air vs with water). I cannot find any other likely or possible area for leakage!

I draw air from an outside window. Is it possible that CO2 media can last for months if it is filtering outside air only?

OP: Realize that with your recirculating system you should be burning thru a lot of media, AND, more importantly, you are depriving your system of fresh air (oxygen).

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EDIT:
Disregard the first part of my previous statement ("Realize that with your recirculating system you should be burning thru a lot of media")....I was thinking of something else. Sorry. Of course you would be using LESS media.

But, consider the second part: "....more importantly, you are depriving your system of fresh air (oxygen)."

 

[Dkmoo]

Thanks Brett and Randy -

i did do a water test before - inside didn't see much change (can't tell exactly b/c using color comparing tester) but outside did see noticeable PH jump from 7.9 to 8.1. I just ordered a PH pen so will do the test again later this week to get more accurate readings.

So, assuming i do have high CO2 - what i'm concerned about is that i have not see the media change color yet in about 10 days now. Since I don't know what a "normal" usage would look like for a recirculating set up with my size, it's hard to judge if:
1) The scrubber is working properly and I'm just not seeing PH change because other sources are pulling CO2 back in, like Randy said, in which case, should I or should I not see color change already in the media by now, OR
2) The scrubber is not working properly b/c the skimmer's air exchange is deficient (and thus no color change on the media). Since the PH cup test indicate that the tank overall is aerated compared to indoor air, this means that air is being exchanged not primarily by the skimmer and i'll need to add a secondary air exchange method hooked up to the scrubber..

Right?

 

[Dkmoo]

thanks Jim - my thought exactly re. the media color change.

One thing to point out is - based on how i understood the scrubber working - recirculating would make media last LONGER, b/c it's not constantly trying to scrub the room's CO2, which for me is high. Open loop would make the media burn faster.

In either case, i also tried to open the loop last couple of days to suck in the "higher" CO2 from the room air, still haven't seen noticable media color change yet - furthering my theory that "skimmer doesn't have enough air exchange".

 

[Dr. Jim]

Thanks Brett and Randy -

i did do a water test before - inside didn't see much change (can't tell exactly b/c using color comparing tester) but outside did see noticeable PH jump from 7.9 to 8.1. I just ordered a PH pen so will do the test again later this week to get more accurate readings.

So, assuming i do have high CO2 - what i'm concerned about is that i have not see the media change color yet in about 10 days now. Since I don't know what a "normal" usage would look like for a recirculating set up with my size, it's hard to judge if:
1) The scrubber is working properly and I'm just not seeing PH change because other sources are pulling CO2 back in, like Randy said, in which case, should I or should I not see color change already in the media by now, OR
2) The scrubber is not working properly b/c the skimmer's air exchange is deficient (and thus no color change on the media). Since the PH cup test indicate that the tank overall is aerated compared to indoor air, this means that air is being exchanged not primarily by the skimmer and i'll need to add a secondary air exchange method hooked up to the scrubber..

Right?

How can you be convinced that there is no leakage? Leakage is easy to detect when dealing with water (e.g. when used as RO/DI) but pretty much impossible when dealing with air.

 

[Dr. Jim]

One thing to point out is - based on how i understood the scrubber working - recirculating would make media last LONGER, b/c it's not constantly trying to scrub the room's CO2, which for me is high. Open loop would make the media burn faster.

One thing to point out is - based on how i understood the scrubber working - recirculating would make media last LONGER, b/c it's not constantly trying to scrub the room's CO2, which for me is high. Open loop would make the media burn faster.

Oh, right....my bad. I was thinking of something else. Sorry.

 

[Brett S]

I might try to do the test inside again, but this time send the air through your CO2 media first. See if you can get a pH increase that way. That would certainly indicate that the media is working.

 

[Dkmoo]

I might try to do the test inside again, but this time send the air through your CO2 media first. See if you can get a pH increase that way. That would certainly indicate that the media is working.

Good point! I'll wait until the ph pen arrive then do that test.

 

[Max_nano]

I put the internal tube with the media in upside down and it won’t bring in air that way. So make sure it’s installed properly with the big arrow pointing up.

Also make sure there is some water in the tiny reservoir at the bottom so it is a humid environment for the media. I use a little dropper to fill that reservoir with some water.

 

[Dkmoo]

Thx Jim - I asked the low oxygen risk in a diff thread. I will definitely monitor any warning signs but the current thinking is that the photosynthesis from the coral/algae plus the air exchange from other sources like the surface and overflow box will at least mitigate this risk.

I'll also add back my chaeto later (doing vibrant now)

I guess once things are working normally ill make the decision of recirculating with the o2 risk vs not recirculating and burn thru media.

 

[Dkmoo]

I put the internal tube with the media in upside down and it won’t bring in air that way. So make sure it’s installed properly with the big arrow pointing up.

Also make sure there is some water in the tiny reservoir at the bottom so it is a humid environment for the media. I use a little dropper to fill that reservoir with some water.

Interesting - I had questioned about that too bc the BRS video and install instrustion suggest that internal media tube was filled from the top but mine fills from the bottom. But the arrow does point up and the rubber washer side is up so I think its installed correctly?

Since its recirculating, the air going into the scrubber is already pretty moist since its coming out of the bubbles from the skimmer.