CO2 and Surface Agitation

I read somewhere that surface agitation will cause a loss of CO2 in water. I recently started using my HOB filter again, which as anyone could imagine, causes surface agitation. I also use a nice air pump with a couple bubble stones throughout the tank. The bubbles agitate the surface substantially.

So, with all that in mind, what sort of loss of CO2 am I looking at? Would it be a few ppm or like 50% or more? Any speculation or "Yeah, Science!" would be appreciated.

 

Losing CO2 due to surface agitation only applies if you are injecting your tank with CO2. If you are not injecting CO2 into your tank, then surface agitation can actually can help to get your CO2 levels back up to the average equilibrium with the ambient air around the tank. Meaning that plants consume the CO2, then your air pumps and HOB filter cause the CO2 to be replenished a little quicker from the CO2 in the air around the tank. At least a little quicker then it naturally would if the water were still.

The CO2 loss happens when you are injecting your tank to hold more CO2 then water naturally would, so it off gasses some of this CO2 due to surface disturbance.

 

I add CO2. My tap water normally runs around 20ppm, which is what I want to maintain. It diminishes to 2ppm within 2 days without supplementation. I'm more-so wondering how much is lost due to agitation compared to plant intake.

 

Hi,
A bit of the science behind it, relates to the principles of gas exchange.

When the surface of the water is agitated (rippling is enough), it promotes the exchange of CO2 from the water for fresh O2.

If my memory serves:
Even the standard air pump does not actually put O2 into the water. It actually creates more surface agitation, promoting more gas exchange, thus increasing O2 concentration.
CO2 is not as easily retained by water, hence when injecting CO2 (DIY or pressurised), a diffuser is typically used to create really tiny bubbles of CO2. Small bubbles take longer to get to the surface, increasing the availability of the CO2 to the plants, before being 'gassed off'.

You can see it for yourself with a simple test. Get a glass of water and a straw. Blow bubbles into the straw, and note how long the bubbles take to get to the surface (pretty quick). Next, get a cue tip, or cotton wool ball, and stuff into the end of the straw. Repeat the bubble blowing, and note the smaller bubbles take longer to get to the surface and gas off.

You can also see it in action with carbonated drinks. Sparkling Wine (Champagne) you can see tiny bubbles rising from the bottom of the glass. Soda/Soft Drink have slightly bigger bubbles. It's this 'gassing off' that makes the drink go 'flat'.

 

Right, but I'm talking about CO2 loss from surface agitation specifically. I understand the concept of smaller bubbles giving a longer surface contact time with the CO2 and water. How much CO2 loss can I expect from surface agitation vs a smooth surface? Do most people with planted aquariums have minimal agitation? What about air pumps?

 

Right, but I'm talking about CO2 loss from surface agitation specifically. I understand the concept of smaller bubbles giving a longer surface contact time with the CO2 and water. How much CO2 loss can I expect from surface agitation vs a smooth surface? Do most people with planted aquariums have minimal agitation? What about air pumps?

In terms of PPM, I can't give you an answer.

I have little to zero surface agitation when my injected CO2 is turned on. My air pumps turn off an hour before the CO2 turns on and then turn back on when the CO2 is turned off for the night.