Skimmers and CO2

[Koty]

We all focus on the fact that high CO2 in the atmosphere went from 0.028% to 0.042% with all its ill effects on coral reefs, and also gets high in closed rooms. However, a key issue, in my opinion, is that CO2 is a heavy gas that is 2.4 times heavier than water. Yet, unlike water, it is still a gas due to its linear molecular structure. The outcome is that CO2 produced by the fauna and flora in our tanks tends to accumulate and not equilibrate with the CO2 in the atmosphere. This provides a sufficient motivation to keep a skimmer, especially in tanks with a heavy bio-load. Besides its central role in keeping the water clean, a Skimmer provides a huge water-air interface, acting as an efficient CO2 exchange apparatus.

 

[Randy Holmes-Farley Verified Community Expert]

Skimmers certainty help equilibrate CO2 (and other gases such as O2) between the water and the air that is entering the skimmer. That can add or remove CO2, and often does different things at different times of the day.

I would say, however, that the “ heaviness” of CO2 has no impact on this equilibration. It neither makes it more likely nor less likely to leave the water. Other aspects do that, such as hydration to carbonic acid, hydrogen bonding to the water, and ionization to bicarbonate and carbonate.

 

[Garf]

a Skimmer provides a huge water-air interface, acting as an efficient CO2 exchange apparatus.

I would suggest that all skimmer exhausts would probably be best vented to somewhere other than a sump. Pretty sure when I've messed with CO2 additions, it would sit on the surface of the sump, locally concentrating it. Even actively venting the whole sump area could probably help.

 

[Randy Holmes-Farley Verified Community Expert]

Even actively venting the whole sump area could probably help.

That’s what I do. Each closed brute can of my sump system has a hole cut for a large bore tubing that sucks air out, keeping the air above the water in each section, including the skimmer section, as fresh as the room air.

 

[Reefering1]

Co2 is heavier than water? Why does it collect at the top of a calcium reactor?

 

[Randy Holmes-Farley Verified Community Expert]

Co2 is heavier than water? Why does it collect at the top of a calcium reactor?

The molecular weight is not playing a role in these issues, but he means one molecule of CO2 weighs more than one molecule of water.

The reason water is a liquid at room temp is because it strongly hydrogen bonds to itself (holding the molecules close together) while CO2 is a gas at room temp because it does not.

 

[Reefering1]

The molecular weight is not playing a role in these issues, but he means one molecule of CO2 weighs more than one molecule of water.

The reason water is a liquid at room temp is because it strongly hydrogen bonds to itself (holding the molecules close together) while CO2 is a gas at room temp because it does not.

Maybe I'm being dense(lol), but i don't understand...
If co2, which is used as a refrigerant, in a static sealed system can be compressed into liquid (and stored at room temp) and evaporates(with a pressure drop)- and those molecules are heavier than h2o, why don't we see co2 bubbles sitting at the bottom of the aquarium?

 

[Randy Holmes-Farley Verified Community Expert]

Maybe I'm being dense(lol), but i don't understand...
If co2, which is used as a refrigerant, in a static sealed system can be compressed into liquid (and stored at room temp) and evaporates(with a pressure drop)- and those molecules are heavier than h2o, why don't we see co2 bubbles sitting at the bottom of the aquarium?

In any situation, gas bubbles are always far less dense than liquids at the same pressure because the spacing between molecules in a gas is huge while in a liquid they are literally touching each other. So in one cubic inch of liquid, there are far, far more molecules than in a cubic inch of gas.

 

[Reefering1]

In any situation, gas bubbles are always far less dense than liquids at the same pressure because the spacing between molecules in a gas is huge while in a liquid they are literally touching each other. So in one cubic inch of liquid, there are far, far more molecules than in a cubic inch of gas.

Thank you, that makes sense...