Airstone dissipates CO2 Into the atmosphere?

[Boot282]

I have a heavily planted high pressure CO2 tank I'd like to change the filtration to sponge filters from a canister. 

Anyone have experience with the CO2 loss by adding air to the tank?  Wondering if the loss is enough to be concerned about. 

Thanks for your reply. 

Edited September 25, 2020 by Boot282
Typo

[FriendlyLoach]

Yes, CO2 is lost when adding an air stone. I am planing to set up a yeast based CO2 injection that runs 24-7. And a Air stone that kicks on at night. 

[Boot282]

Thanks for the reply FriendlyLoach. 

I've also read there is some CO2 loss but I wonder how much there really is. If it's a small percentage, it would be worth it for my situation. 

I'll search around and see if I can find real numbers.I

[Antichton]

I'd say the effect should be pretty small. The CO2 loss is probably proportional to the surface area of water exposed to air, which is going to be the surface of your tank (length x width) + the surface area of the bubbles.

Not sure how accurate this site is (just googled it), but they give the approximate bubble size as "pancake shaped disks 0.16" in diameter", which has a surface area of about 0.053 sq in. And I counted maybe ~40 bubbles per inch of height in the pic of the airstone (assuming the airstone is about 1" long).

So for something like a 20 gallon high tank, you'd have an unaerated surface area of 24"x12" = 288 sq in. You'd get an approximate surface area from aeration equal to the surface area of each bubble x the number of bubbles at any given time. From my estimate above, this gives a "bubble surface area" of 0.053 x 40 x 16 = 34.1 sq in. which is ~12% more surface area/CO2 loss compared to no aeration. 

Of course this is all guesstimation using data from a random website I googled so it could be completely wrong...

[Boot282]

Antichton, I appreciate the well thought out response and the link –

From what I have read in the past and reading the info you provided along with the info in this link, https://www.2hraquarist.com/blogs/choosing-co2-why/how-to-push-the-limits-of-co2-safely  it seems to me the larger the bubble (and fewer of them for the same volume of air), the less efficient in creating surface agitation (for gas exchange).  For my purposes this is a good thing.

I’m going to assume running a sponge filter (at my typical rate) without an air stone produces a bubble that is about ½ inch in diameter when its breaks the surface (due to the pancake shape).  The surface area of each bubble would be about 0.2 sq in.  I would estimate there’s only room for about 5 bubbles per inch of height.

Using your example of a 20 high, the bubble surface area would be 0.2 (sq in.) x 5 (# of bubbles per inch) x 16 (height of the tank) = 16 sq in. which increases surface area by about 6%.

This falls well into my acceptance of how much the CO2 loss increase would be using sponge filters vs a canister.

Hopefully, there’s enough errors in here to cancel each other out producing a somewhat accurate result!

Edited September 25, 2020 by Boot282

[Ryan W]

First off, I'm far from an expert and hold no academic degrees. Second, I think you're way over thinking this. Third, I agree with Antichton about it more than likely being proportionate to the surface area of your tank in relation the surface area of the bubbles. Example: An airstone in a 2.5 gallon tank is going to cause much more surface agitation than if that same airstone was in a 250 gallon tank. As far as how detrimental that co2 loss is, well, I suppose that's why most co2 regulators come with needle valves. Use that to compensate for the loss. Should you worry about it? Yes. However, that's what that needle valve is for.

Tom Barr injects a lot of co2 (or injected, I haven't heard much about him in a long while) and he usually also implements a sump on his tanks and he is pretty much known as the high-tech planted tank guru. I believe I recall a post very similar to your post on Barrreport a long time ago about co2 loss with the overflow of the sumps and Barr's response was essentially that (and I'm paraphrasing here) "yeah, there is a loss but its nothing that cant be regained by properly adjusting your needle valve".

I don't know how big your tank is but another thing to consider about going from a canister to a sponge filter is retaining the amount of current that the filter produced in order to fully saturate the entire water column with co2 and, in conjunction, the efficiency of how you're diffusing the co2 (are you using an inline-atomizer, in-tank ceramic disk, reactor?).  Just make sure you aren't creating any dead spots or a lower co2 saturation by only using the sponge filter. Say you're using a ceramic disk diffusor. Those rely heavily on the output of your filter to mix those bubbles within your tank and if you decrease the tank current enough, those co2 bubbles are just going to rise to the surface and pop. You still want all areas of your tank to receive flow and in essence, co2. Considering you won't have a pump to circulate your filtered water, an in-line atomizer or a reactor is out of the question. You can get in-tank atomizers (I think they are called "bazooka" atomizers?) that would create a finer mist of co2 that wouldn't be as prone to just raise and pop. Again, as long as you can ensure co2 dissolution and good tank current, I believe the "math" here to be mostly arbitrary. Take it by ear and adjust accordingly whenever needed. Adjustability is one of the main benefits about using a pressurized co2 system. You are in control. If you need more, add more. if you need less, add less. As the aquarist, we get to dictate how much of what gets introduced into our tanks and its very much ok to take advantage of those options when we need to. This is a great example of knowing when to deploy those advantages by increasing co2 output to compensate for co2 loss from the increased surface agitation. What would all of that look like as an equation? I couldn't even in the least begin to understand any of that but fortunately for us, we don't ever really need to. 

Lastly, I have to ask, why the need to change your setup? Are you having issues or do you just want to switch things up a bit? 

 

[Boot282]

Ryan,

To answer the questions first.  Standard 75 gallon tank. FX-6 canister filter. CO2 diffuser ceramic disk from Aquarium Co-op placed under the output of the filter.

Simplicity and consistency is why I'm thinking of changing to sponge filters in this tank. I currently have 8 aquariums set up and use sponge filters in all but this one and one other. The FX-6 is a great filter except when it needs to be cleaned.  Changing everything to air powered sponge filters saves me the canister cleanings and probably saves me some electricity expense. One of the valid points you bring up is on the current I would be losing with sponge filters. I will need to consider that if I switch out the canister.

The reference to Tom Barr is great as  back in the early 2000's or thereabouts he shared a ton of knowledge and helped many (including myself) achieve success in planted aquariums.  The over thinking is true - the math is probably way off but it was a fun way of thinking about my original question of how much CO2 is really lost with surface agitation. 

And finally, will take your advice and adjust that needle valve accordingly to compensate for the loss if I do end up with sponge filters in this aquarium. 

[Cory]

Lots of things kinda glossed over here. Really you'd only be gassing out co2 if the concentration of co2 is higher than what the airstone was replacing. Plenty of times people are limited as their tank has  used up all the co2 in which case an airstone actually adds in co2. 

As far as having an airstone and co2 injection going, having one doesn't affect the other. You could have max co2 saturation and oxygen at the same time. THe act of bubbles moving up the water column and breaking the surface would gas off some co2, maybe you put a few percent more co2 into the system and now you have achieved a healthy environment for fish and plants. 

Co2 uptake would be another big factor, which most people aren't measuring and instead just say any agitation is bad, co2 good. Meanwhile lots of people end up at the edge or worse for their fish with talk like that. Think of it this way, an airstone keeps your fish alive, co2 keeps your plants alive, instead of choosing 1 to live why not both? As it's super easy to accomplish both being in good supply in our aquariums.

[yannachka]

i personally run some form of extra air (sponge filter, air stone, etc) in all my tanks with co2 just in case i was fiddling with the needle valve and accidentally set it a little too high. i havent seen any negative effects in terms of the plants and the positives far outweigh the small amount that may gas off. i find extra air also helps circulate the water better in the tank (depends on the size/surface area of course) which helps with dispersing the co2 and making sure any ferts added reach all of the plants. i actually have a small powerhead above the diffuser in my goldfish tank to push the gas across the tank as it comes out, over the months of doing this ive seen better growth in my plants on the other side of the tank. 

i think people are too scared of air, potentially needed to refill the canister maybe a day earlier doesn’t offset all of the positives that air adds to a tank in my opinion. 

[thatgaljill]

I'm so glad to have found this forum and  topic! Tagging into it ... I have an Aqueon 14 with a small aquarium co-op sponge filter and never clog air stone in it and would like to add CO2 with a nano pressurized system.  If the sponge filter is in the front right corner, should I place the diffuser in the back left corner?