pH from Skimmer - Outside Air or CO2 Scrubber

[markstubb]

So I have a question that I can't seem to figure out the answer to. I have a SVS3-24 Life Reef venturi non-recirculating type skimmer and have been trying to get my pH to stay over 8. When I first set up my tank, it would drop to 7.5-7.6 at night, a high at 7.85 or so. After a while I decided to take action. I currently have the tank in a rental, so I didn't want to drill a big hole in the wall for a fresh air intake pipe for my skimmer, so I went out and got some CO2 scrubbing media, aka soda lime.

I improvised a reactor by putting a john guest type fitting into the lid of the CO2 media container and drilled a bunch of small holes in the bottom of the container. Hooked it up to my venturi input and blam - overnight I had pH maxing out around 8.17 and low end of 8.05. Sweet. It works. Well, after a few months, I just got tired of buying the media, monitoring it, the pH drop when it suddenly stopped working, and most importantly, the cost. I decided that since scrubbing the indoor air of CO2 resulted in such a pH boost, that surely running a line outside for the skimmer would solve my issues, so I went ahead and drilled the hole, ran a 1/2" ID flexible pipe outside, put a canister type carbon block filter inline and hooked it up to the skimmer.

Over the next few days I monitored the pH and it MAXES out at 8. While it's an improvement, it's not what I saw with soda lime.

What gives? I can't imagine the outside air has that much more CO2 than what the scrubber removes. Maybe I can run a scrubber inline to the external air and it'll last a lot longer as there's less CO2 to scrub?

And, there's always the option of just not caring - that pH between 7.8 and 8 is no big deal and I should just quit obsessing over it (which I still don't get why I have a decent swing every day - I have a decent sized fuge with chaeto growing like mad, with an opposite light schedule).

 

[Reefing Madness]

 

[ca1ore]

I would go with the 'quit obsessing over it' option

Neither fresh air line nor CO2 scrubber ever made much difference to the pH in my tank (though better circulation through my basement fish room did). My tank is an open top, highly circulated system so thinking that the skimmer line would offset all that water sitting in a high CO2 environment is foolish - large volume replacement of room air does help though, as one would expect. FWIW, I would expect a scrubber to outperform a fresh air line because even outside air contains some level of CO2. Run outside air through a scrubber and the media still depletes, just not as fast.

 

[blkhwkz]

I have an outside air line connected to my scrubber and then skimmer. I get 10 days to a few weeks out of a canister depending on the time of year. I just buy the soda lime from vet supply place, 5 gallon container looks like it will last me over a year. Bought it last June and still have enough to refill a few more times. I bought the BRS stuff to see if it lasted longer and it lasted as long as the vet supply stuff, but costs a lot more.

 

[markstubb]

I would go with the 'quit obsessing over it' option

Neither fresh air line nor CO2 scrubber ever made much difference to the pH in my tank (though better circulation through my basement fish room did). My tank is an open top, highly circulated system so thinking that the skimmer line would offset all that water sitting in a high CO2 environment is foolish - large volume replacement of room air does help though, as one would expect. FWIW, I would expect a scrubber to outperform a fresh air line because even outside air contains some level of CO2. Run outside air through a scrubber and the media still depletes, just not as fast.

I totally agree with your thought process, but I tried to word my question differently than the ones you’ve kindly addressed before related to this. What I’m trying to understand is why a co2 scrubber alone so drastically outperformed a fresh air intake. The outside air can’t have THAT much CO2....right?

 

[markstubb]

I have an outside air line connected to my scrubber and then skimmer. I get 10 days to a few weeks out of a canister depending on the time of year. I just buy the soda lime from vet supply place, 5 gallon container looks like it will last me over a year. Bought it last June and still have enough to refill a few more times. I bought the BRS stuff to see if it lasted longer and it lasted as long as the vet supply stuff, but costs a lot more.

I’m not sure if I have that option available to me given my location, but I’ll look around for some bulk supplies rather than the CDX media I was using. I will also make a proper reactor if I go this route. I’ll likely use a generic water filter canister and one of those refillable cartridges meant for DI resin.

But. I need to probably just get over it. I just like to tinker

 

[ca1ore]

I totally agree with your thought process, but I tried to word my question differently than the ones you’ve kindly addressed before related to this. What I’m trying to understand is why a co2 scrubber alone so drastically outperformed a fresh air intake. The outside air can’t have THAT much CO2....right?

Last two sentences of my prior post? I don't know how much more CO2 the outside air would have to have to give the results you are seeing; maybe just a little more IS enough? Figure nominally that the outside air has 400 ppm of CO2 (maybe even a bit higher); what does the post scrubbed air contain? Is it zero, dunno; but perhaps lower enough to give you the results you see.

 

[rossco]

Maybe ask to have this moved to the Reef Chemistry forum or repost there?

 

[blkhwkz]

I’m not sure if I have that option available to me given my location, but I’ll look around for some bulk supplies rather than the CDX media I was using. I will also make a proper reactor if I go this route. I’ll likely use a generic water filter canister and one of those refillable cartridges meant for DI resin.

But. I need to probably just get over it. I just like to tinker

Hadn't noticed your location before, perhaps you get get it from diving supply place? It is used in rebreathers so might be able to get it in bulk that way.

 

[Randy Holmes-Farley]

I totally agree with your thought process, but I tried to word my question differently than the ones you’ve kindly addressed before related to this. What I’m trying to understand is why a co2 scrubber alone so drastically outperformed a fresh air intake. The outside air can’t have THAT much CO2....right?

lol

The outside air might have twice or 10 times as much CO2 as the scrubber, depending on how effective it is. Or maybe even less than a scrubber.

 

[markstubb]

Thanks @ca1ore and @Randy Holmes-Farley . I suspect you're right - I guess I wanted someone to confirm that outside air isn't as void of CO2 as one would think. Wonder if it's cheaper to just pipe an oxygen tank into the scrubber (kidding, I don't need an explosion in the house if it disconnected). If I had some sort of CO2 meter available to me, I'd love to test it out as I'm very curious about the result - which I suppose I'm testing right now through the skimmer and the pH is the metered result.

@blkhwkz That's a good idea - I'll see if I can ask around on Facebook.

On a side note, I'm noticing that the skimmer is performing much better with the fresh intake. Not exactly sure why but the skimmate is much more consistent and nastier than prior to the fresh intake and/or the scrubber.

 

[SteadyC]

Does your outside line connect to the silencer, or directly into the pump? I found when connected to the silencer, there is ambient air can be pulled through seams of the silencer. At least the one I have, doesn’t seem glue sealed. This lead to not much PH affect on my tank from the line connected to outside. When I connected the scrubber directly to the pump, that made me wonder if I should have connected the outside line directly to the pump, rather than the silencer. Haven’t tried going back to the outside line, but connected directly to pump, it’s spring now and everyone around sprays their trees with beetle killer, or staining their cedar siding.

 

[markstubb]

I have no silencer as it connects directly to the venturi inlet. LifeReef skimmers don't use silencers like most needlewheel styles as they recirculate the air for the venturi.

 

[markstubb]

Also, I have a carbon block inline, so I hopefully should be filtering out any external pollutants.

 

[SteadyC]

I have no silencer as it connects directly to the venturi inlet. LifeReef skimmers don't use silencers like most needlewheel styles as they recirculate the air for the venturi.

Aw, ok. I’m not familiar with venturi’s

 

[markstubb]

it's just a plastic T that draws water in one side and has a small orifice vented to the air that, due to the suction from the water, injects bubbles into the water as it passes by the orifice.

 

[Randy Holmes-Farley]

Thanks @ca1ore and @Randy Holmes-Farley . I suspect you're right - I guess I wanted someone to confirm that outside air isn't as void of CO2 as one would think. Wonder if it's cheaper to just pipe an oxygen tank into the scrubber (kidding, I don't need an explosion in the house if it disconnected).

The most effective combination is a scrubber using outside air. The media lasts longer and the CO2 level is likely lower than using indoor air on the scrubber.

FWIW, adding O2 does nothing for pH. Only CO2 addition/removal impacts it, and adding or removing one does not have any effect on the other.

 

[markstubb]

Wow, @Randy Holmes-Farley . That’s interesting. So you’re saying if I pumped O2 into the skimmer that pH wouldn’t be affected?

 

[Randy Holmes-Farley]

Wow, @Randy Holmes-Farley . That’s interesting. So you’re saying if I pumped O2 into the skimmer that pH wouldn’t be affected?

That is correct. O2 has no effect on pH.

If you know the carbon dioxide level and the carbonate alkalinity, you can directly calculate the pH.

This has more:

pH And The Reef Aquarium
http://www.reefedition.com/ph-and-the-reef-aquarium/

and for the math part:

Chemistry And The Aquarium: The Relationship Between Alkalinity And pH ? Advanced Aquarist | Aquarist Magazine and Blog
https://www.advancedaquarist.com/2002/5/chemistry

 

[Reef Dude]

Following along. I’ve seen the same issue in the past. When I hooked up my slimmer line to outside air, I saw minimal effect. When I added the CO2 scrubber, I saw a large effect (ph bottoms out at 8.15 rather than 7.75 like it used to). My skimmer sucks a lot of air, and I used to burn through a canister of soda lime every 3 days... this was not sustainable from a cost standpoint, even with purchasing 5-gallon buckets through med vet. One thing I learned on R2R that helped is adding humidity to the CO2 scrubber intake. Some hook the scrubber intake to draw air from the skimmer cup. In my case, I filled a typical ro canister with water and put it inline before the scrubber. So outside air now passes through the canister filled with water, through the scrubber, then into the skimmer. By doing this, I’ve extended the life of the soda lime from 3 days to a 1.5 weeks.

But to your initial point, I don’t understand why the outside air line alone doesn’t solve ph problems (or perceived problems). For example, opening the windows to the house makes my ph jump to 8.3, but drawing fresh air through my skimmer has minimal impact. It’s interesting to think about though.