Recirculating CO2 scrubbing versus standard pros and cons

[wanderer]

I tried searching to see if anyone posted about the pros and cons of standard versus recirculating and didn’t see any results.

I’ve been trying to boost my pH as Im interested in growing stony corals. It seems that faster growth of corals (likely related to easier precipitation of calcium carbonate) is the only reason to boost pH ( I suppose if one has clams this may apply also but I don’t have any interest and can’t say I’ve looked into it). Unless someone’s pH is 7.5 or under boosting pH has no effect on fish.

In my opinion recirculating scrubbers cause more trouble than they solve unless you have a lot of failsafes (solenoids, float switch to turn off skimmer if it overflows or just draining the draining the skimmer externally)

They seem to work in a closed loop so you’re basically lowering the CO2 and then sealing off the skimmer and thereby a huge chunk of air exchange so that you’re wholy dependent on surface air exchange for other gases (mainly O2, but I suppose if you have other gases such as H2S from anaerobic metabolism then off gassing is limited, though this is probably not a very common scenario)

It seems the main benefit is lower usage of media which can be quite cost saving. Some people report huge pH boosts though that seems inconsistent.

Standard CO2 scrubbing still gets the majority of the results in that a you still get a large pH boost without the potential for nuking your tank if you have an overflow of skimmate into your line. The most common problem is inefficient scrubbing if the airflow is too dry. running the intake tubing into a water filled jar seems to humidify the air adequately (example below)

My pH went from around 7.9 on average pre scrubber to 8.1 with a scrubber. Surprisingly when I tried to recirculate I did not get any additional pH boost. Using sodium hydroxide as my alk source has given me an additional boost of 0.05, while not huge is still a decent boost with really not additional effort.

IMO for most people going from non recirculating to recirculating has a decent chance for a catastrophic failure while only providing a modest pH boost though it does save quite some money on media. You also lose a lot of oxygenation and if you have a high fish load that can be potentially catastrophic as well

Curious what others think

 

[Randy Holmes-Farley]

I am one of the few people posting cons, which is lack of oxygenation when using full recirc.

 

[wanderer]

I am one of the few people posting cons, which is lack of oxygenation when using full recirc.

Yeah I did see you mention that in a couple of the threads I came across.


Though most of the threads on the topic are otherwise almost entirely supportive of recirculating even though the pros seem to be not that strong.

i think measurability bias plays a huge role since we can’t typically measure O2 though it seems a poorly oxygenated tank can have low enough O2 that a high bioload tank may become hypoxic. I’d imagine that having high pH would also suppress respiratory drive of fish even in the case of low O2

 

[jda]

The other con of a recirc is that if you need to rely on surface gas exchange to boost o2, then you welcome in more air from the home which is likely high in co2 and why you have low pH in the first place.

Don't pay any attention to me, though... I have no idea why people don't just open some windows afraid of the pennies heating their home, yet they will spend hundreds on media and a reactor. IMO, people just want to play with toys and things... and recirc sounds cooler. If you were around long enough, you saw the fad of recicurlating skimmers, which were sworn by some to be SOOOOO much better with all of the contact time and pseudo-science and stuff... yet you cannot hardly find one now.

 

[wanderer]

The other con of a recirc is that if you need to rely on surface gas exchange to boost o2, then you welcome in more air from the home which is likely high in co2 and why you have low pH in the first place.

Don't pay any attention to me, though... I have no idea why people don't just open some windows afraid of the pennies heating their home, yet they will spend hundreds on media and a reactor. IMO, people just want to play with toys and things... and recirc sounds cooler. If you were around long enough, you saw the fad of recicurlating skimmers, which were sworn by some to be SOOOOO much better with all of the contact time and pseudo-science and stuff... yet you cannot hardly find one now.

I completely agree with you that the whole diy aspect attracts a lot of people. I definitely enjoyed the minor modifications I made to my skimmer cup top to make it into a recirculating skimmer though I ended up not really using it.

I think if one is close to a window then running an airline to the window basically costs nothing and will boost the pH a nice amount. However the downside is that the pH will likely max around 8.1 or so at the dkh that we typically run for reef tanks and while that is okay, some people do wish to aim for a higher pH. In my case the tank is about 15 feet and I don’t want to run an ugly tube across my living room and out a window.

I will probably keep my windows open as much as I can when the weather is better. But during the winter my heating bill is already have a few hundred a month and opening a window will make that go up quite a lot (dang electric baseboard heaters)

 

[jda]

I'll bet that if you wait until the temp is in the 40s and open a door at each end of the home for one minute a day that you can do more than a co2 scrubber will and not even have your heating bill rise a dollar a month... if that. You just have to exchange air, not cool the home down.

For me, the benefits of better sleep and never anymore headaches is worth any cost, but exchanging air is almost free.