Recirculating CO2 Scrubber and Oxygen Levels

[reddogf5]

I have a recirculating CO2 scrubber on my skimmer, and never considered O2 levels - is this something to be concerned about? Is there a way to add oxygen, short of an oxygen tank, or another way to raise pH? Also, is there an inexpensive way to measure oxygen content in the water? The tank is pretty closed up, with glass lids in the winter. I tried outdoor air, but there is no good way to plumb it in, and pollen season makes the skimmer overflow.
Could hydrogen peroxide help?

 

[taricha]

I agree that it's a concern to think about. Aeration is an important role for skimming, and cutting off new air flow into the skimmer may impact that.
(I haven't seen any measurements for what happens to O2 if you make skimmer recirculate the air, and have a glass lid over the top.)
You can get an O2 probe or a O2 chemical test. The probe is less hassle.

If you had an O2 measuring device, then h2o2 may be an interesting workaround.

 

[piranhaman00]

My experience

https://www.reef2reef.com/threads/recirculating-co2-skimmer-reminder-warning.921877/

 

[Clownfishy]

A few years back, I recycled the air on the skimmer very briefly but then quickly removed it because of the comment @Randy Holmes-Farley made in this thread. I still scrub the air going into the skimmer but have never tried recycling the air for this very concern
https://www.reef2reef.com/threads/my-experience-raising-ph.394826/page-2

 

[Randy Holmes-Farley Verified Community Expert]

I would be concerned about O2 at night if the skimmer is full recirculating.

 

[taricha]

My experience

https://www.reef2reef.com/threads/recirculating-co2-skimmer-reminder-warning.921877/

This seems a pretty good demonstration of exactly what I would be worried about doing something that removes the aeration function of a skimmer. Thank you for sharing.

 

[reddogf5]

I would be concerned about O2 at night if the skimmer is full recirculating.

I ordered a Salifert O2 test, is there any range to expect O@ to be in, or a lower limit?

 

[taricha]

I ordered a Salifert O2 test, is there any range to expect O@ to be in, or a lower limit?

max O2 in saltwater is 6-7mg/L depending on temperature.

 

[Randy Holmes-Farley Verified Community Expert]

Eric has a lot of O2 discussion and data in these articles:

The need to breathe in reef tanks: is it a given right?
http://www.reefkeeping.com/issues/2005-06/eb/index.php

The need to breathe, part 2: experimental tanks.
http://www.reefkeeping.com/issues/2005-07/eb/index.php

The Need to Breathe, Part 3: Real Tanks and Real Importance
https://reefkeeping.com/issues/2005-08/eb/index.php

 

[Steve2020]

Eric has a lot of O2 discussion and data in these articles:

The need to breathe in reef tanks: is it a given right?
http://www.reefkeeping.com/issues/2005-06/eb/index.php

The need to breathe, part 2: experimental tanks.
http://www.reefkeeping.com/issues/2005-07/eb/index.php

The Need to Breathe, Part 3: Real Tanks and Real Importance
https://reefkeeping.com/issues/2005-08/eb/index.php

Thanks for posting the links Randy. Made for some very interesting reading. What I found interesting is that tanks under 75gal seem to benefit from skimming and and air stones to where the larger tanks seem to benefit more from having a larger surface area and reverse lighting and little benefit from the hobby sized skimmers and air stones. Photosynthesis seems to be the number one factor affecting % of O2 saturation on larger tanks. One thing I did not notice or maybe I missed it is what is the lowest % acceptable O2 saturation value? Do you have an opinion on what that value would be?

 

[reddogf5]

Got a Salifert O2 test kit today, read 8 this afternoon, will check again tomorrow morning before the lights come on.

 

[reddogf5]

Measured my tank this morning, looked closer to 6 than 8, so let's call it 6 mg/l. I think at this point I'm not going to worry about it, will recheck if fish count goes up.

 

[Randy Holmes-Farley Verified Community Expert]

Measured my tank this morning, looked closer to 6 than 8, so let's call it 6 mg/l. I think at this point I'm not going to worry about it, will recheck if fish count goes up.

What level would have caused you to worry?

I'd personally aerate some tank water for an hour or so nd measure it to see what full saturation reads in that setting.

Here's what I found for my tank system in the context of seeing what effect ozone might have. There was a drop at night vs day. I was using a big non-recirculating skimmer.

I obtained the following test results before and after using ozone in my system:

Before ozone:
Main 120-gallon tank just before lights on: 5-6 ppm O2
Main 120-gallon tank just before lights off: 6-7 ppm O2
Refugium 1 (always lit) just before main lights on: 6-7 ppm O2
Refugium 1 (always lit) just before main lights off: 6-7 ppm O2
Refugium 2 (always lit) just before main lights on: 6-7 ppm O2
Refugium 2 (always lit) just before main lights off: 6-7 ppm O2

After ozone:
Main 120-gallon tank just before lights on: 6 ppm O2
Main 120-gallon tank just before lights off: 7 ppm O2
Ozone tubing reactor effluent after activated carbon: 6-7 ppm O2
Sump just before lights off: 7 ppm O2

A strict reading of the values that I obtained suggests a small rise of between 0 and 1 ppm in O2 in my main tank. However, the kit is hard to read in the 5-8 ppm range, so the oxygen could have risen by 0-1 ppm, or more, or perhaps not at all. The effect, if real, may be much larger in an aquarium where the oxygen drops much more at night (i.e., those without refugia lit at night or those with less aeration).

 

[reddogf5]

The test kit suggested a minimum of 6 ppm for marine, so if it went below that I would do something. Measuring the fully saturated state is a good idea, I will do that.

What level would have caused you to worry?

I'd personally aerate some tank water for an hour or so nd measure it to see what full saturation reads in that setting.

Here's what I found for my tank system in the context of seeing what effect ozone might have. There was a drop at night vs day. I was using a big non-recirculating skimmer.

I obtained the following test results before and after using ozone in my system:

Before ozone:
Main 120-gallon tank just before lights on: 5-6 ppm O2
Main 120-gallon tank just before lights off: 6-7 ppm O2
Refugium 1 (always lit) just before main lights on: 6-7 ppm O2
Refugium 1 (always lit) just before main lights off: 6-7 ppm O2
Refugium 2 (always lit) just before main lights on: 6-7 ppm O2
Refugium 2 (always lit) just before main lights off: 6-7 ppm O2

After ozone:
Main 120-gallon tank just before lights on: 6 ppm O2
Main 120-gallon tank just before lights off: 7 ppm O2
Ozone tubing reactor effluent after activated carbon: 6-7 ppm O2
Sump just before lights off: 7 ppm O2

A strict reading of the values that I obtained suggests a small rise of between 0 and 1 ppm in O2 in my main tank. However, the kit is hard to read in the 5-8 ppm range, so the oxygen could have risen by 0-1 ppm, or more, or perhaps not at all. The effect, if real, may be much larger in an aquarium where the oxygen drops much more at night (i.e., those without refugia lit at night or those with less aeration).

 

[reddogf5]

In case there is any interest, I aerated some tank water Sunday, for about an hour and a half and it tested between 6 and 8 (the shade of pink scale is a little hard to judge)

 

[Randy Holmes-Farley Verified Community Expert]

In case there is any interest, I aerated some tank water Sunday, for about an hour and a half and it tested between 6 and 8 (the shade of pink scale is a little hard to judge)

Thanks for the update! :)

 

[VelocityTech]

In case there is any interest, I aerated some tank water Sunday, for about an hour and a half and it tested between 6 and 8 (the shade of pink scale is a little hard to judge)

Have you done any more testing with results?

 

[BCash74]

I've recently been researching this topic for my own personal application. I figured I would continue this post instead of starting another. I apologize if question has been answered somewhere else; in my defense, I cannot get the above links by Eric/reefkeeping to open...

In my early years of reef keeping I utilized skimmers made by Jeff at Lifereef.com. I suspect they are not as popular as they once were - although I could be completely wrong on this. Lifereef made a pretty well-regarded product (at least in my reefing circles back in the day). Anyways, his skimmer utilizes a venturi with the air intake coming out of the skimmate collection cup. It was not done this way in order to utilize a CO2 scrubber, but for other reasons that Jeff felt contributed to the function of the skimmer. I ran mine on 3 different evolutions of my reef from 2003-2012. Started with a 90 gallon, finished with a 285 gallon tank.

Would anyone agree that the "net effect" of this set-up would be a lot like not running a skimmer at all - in regards to aeration specifically? The same air essentially circulated in the skimmer again, and again, etc....

Why do I ask (especially a topic that has been brought up on numerous threads)? I've recently added a BRS scrubber to my skimmer and my pH went from 7.9-8.1 to 8.2-8.3 very consistently. Reefing creates a lot waste by necessity and can be price prohibitive for some. Changing my CO2 media every 8-10 days (what I'm averaging) seems like any easy way to reduce waste and decrease my maintenance routine a bit. The cost is not an obstacle for me, but an easy way to save a couple bucks. I've read the pros/cons and the concerns in regards to low O2 with a recirculating scrubber, but my thoughts keep coming back to my old Lifereef skimmer - I'll post some photos, but I had some great tanks when I ran that skimmer. I've never heard anybody raise concern over the Lifereef design because it could lead to lower dissolved oxygen levels.

Thoughts?

 

[BCash74]

My first set-up running a lifereef skimmer on a 90 gallon tank.... in regards to fish, I had the yellow tank, foxface, 3 or 4 chromis', 2 clowns, and possibly a royal gramma.

Same lifereef skimmer run 5 years later on a 285 peninsula. Not evident in this photo, but I had 3 tangs, a school of chromis', 4 or 5 lyretail anthias, and pair of clowns.

Point of the photos is to show that I had pretty good success running a skimmer which effectively was not aerating the tank in a meaningful way - or am I thinking about this the wrong way?

 

[Randy Holmes-Farley Verified Community Expert]

My first set-up running a lifereef skimmer on a 90 gallon tank.... in regards to fish, I had the yellow tank, foxface, 3 or 4 chromis', 2 clowns, and possibly a royal gramma.

Same lifereef skimmer run 5 years later on a 285 peninsula. Not evident in this photo, but I had 3 tangs, a school of chromis', 4 or 5 lyretail anthias, and pair of clowns.

Point of the photos is to show that I had pretty good success running a skimmer which effectively was not aerating the tank in a meaningful way - or am I thinking about this the wrong way?

Tank top aeration can oxygenate many tanks. So can reverse lit refugia. But the question with every husbandry action that is justified by a tank it is used on is whether the single action in question helps, hurts, or is unrelated to the tank success.

In this case, knowing oxygen levels at night would, I think, be more useful to ***** the concern than noting the number and type of fish in the tank, since fish are among those most likely to be impacted.