[Bananableps]

I'm a little confused with the logic. Did you put the airstone in just to get rid of the film? What does plant competition for CO2 have to do with this? The air stone will only remove CO2 from the water, starve your plants more, and reduce the oxygen production further.

The film on your water is perfectly natural. It's just bacteria and protozoa. Biodiversity ftw. If it's aesthetically unpleasing, just swish your hand around the surface every morning, or get a very very tiny water pump to create surface agitation.

 

[Bluebugs]

The film doesn't disgust me, but I would prefer for it not to be there, the staleness of the water does invite algae as well, which is not fun.

As for gassing off CO2, isn't it just injecting normal air into the water, which includes CO2? It's not like I have it hooked up to an Oxygen tank.

 

[jrill]

Air stones don't inject air into the water. The surface activity it causes will help increase oxygen and increase the speed the CO 2 is outgassed.

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[Bluebugs]

So they are of no use in low tech Planted tanks? Kind of a shame, I think they do a fantastic job moving the current around, not too much, but keep it from going stagnant.

How do they compare to a sponge filter, in terms of out-gassing CO2? I would think they would have the same effect, no? I use sponge filters in one of my tanks and the plants are doing great.

 

[THE V]

In the low tech setting, increasing the circulation increases the CO2 concentration. Increased circulation only causes issues with outgassing when you are injecting the CO2.

An airstone wount be fine. If you don't like the sound of air pump (they can be loud), they sell small water movers for marine tanks that work great.

 

[Bluebugs]

You seem to contradict yourself. You say it's only an issue if you are injecting CO2, but then recommend against it. Was that a typo? I'm not trying to be a jerk, I just want a grasp on things.

 

[THE V]

Low tech = non CO2 injected. In this situation all of the CO2 the plants are getting is from the atmosphere.

As the plants eat the CO2 from the water, more C02 from the atmosphere diffuses into the tank. Water circulation helps speed this process up by increasing the amount of water molecules in contact with the air over any time period. Ripples on the surface also increases the surface area of the water in contact with the air.

In a low tech tank where CO2 is the limited, good circulation can have significant impact in growth.

This is all basic physics of gasses and liquids if you want to do some research.