# Effect of nighttime aeration in non-CO2 tank?



## upikabu (Sep 2, 2005)

Hi All,

What effect does nighttime aeration have on a non-CO2 tank? My non-CO2 tank has been doing well for over 6 months with very little surface movement (the Eheim spraybar is placed below the water level). However lately I've been noticing an increasing amount of green scum/oil forming on the surface about 2 weeks after each water change. I saw on some posts here that turning on an air pump at night will help reduce surface scum. I know plants don't need the CO2 at night, but my concern is that nightly aeration (or even surface movement for that matter) may cause the level of CO2 to fluctuate enough to be detrimental (somehow) to plants in a non-CO2-added environment. 

The thing that confuses me is how surface movement/gas exchange really affects non-CO2 tanks in the first place. Wouldn't the CO2 level in these tanks be the same (or similar) to atmospheric CO2 anyway? If so, it shouldn't really matter whether or not these tanks have a lot of surface movement. What's the basis of the recommendation to top up evaporation in non-CO2 tanks? I'm probably missing something obvious - hoping someone can enlighten me here! 

TIA & Cheers!

Background: The tank is a well-planted 42g with low-light (1.7wpg). It gets water change every 1-2 months and a weekly dose of Equilbrium and a little bit of macros. The fish and food waste provides the rest of the nutrients. Plant growth is slow but steady, and I hardly see any algae.


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## trenac (Jul 16, 2004)

There is no need to worry about surface agitation in a non C02 tank.

Surface scum is usually caused from buildup of proteins in the tank. Surface agitation will help. So will a surface skimmer or Molly's.


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## John N. (Dec 11, 2005)

You definately can rid of surface sucm by aggitating the surface since what that does is stir it back into the main body of water.

In regards to the why surface aggitation outgases CO2, the reason is pretty simple, and it seems like you have an idea about it. The aggitation moves the water around allowing more surface exchange with the atmospheric air. There's usually more CO2 in the tank since we inject it, than the air does. So the outgasing takes place, and the CO2 diffuses from high concentrations to low. So we don't want that, so that's why we typically don't create alot of surface movement.

-John N.


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## upikabu (Sep 2, 2005)

Thanks for your replies, Trena & John! 

If surface agitation doesn't matter for non-CO2 tanks, would having an air stone on all the time be bad for these tanks? I know the general recommendation is no air stone for planted tanks b/c it will drive the CO2 out. But in a non-CO2 tank, wouldn't the air stone promote better gas exchange, thus ensuring that CO2 level in the tank remains the same as atmospheric level?

One possible explanation is that in a heavily planted tank with no surface agitation the amount of CO2 generated by the plants at night is enough to feed the plants during the day. If true, this would mean that having an airstone at night would be detrimental to the plants as it would drive off the CO2 produced at night, not leaving enough for photosynthesis during the day. Am I way off track here?


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## dennis (Mar 1, 2004)

An airstone would not be necessary. Simply raising the spray a little so you get some surface movement woudl work fine. Incedently, surface movement is best in a non-CO2 setup as the plants can use up the CO2 in the water VERY quickly. So, adding surface movement actually helps maintain consistant CO2 levels through out the day.

Now, lets see some photos of this tank!


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## Raul-7 (Feb 4, 2004)

Although it is somewhat true, I will have to disagree. I currently run a non-CO2 tank with a spraybar and a powerhead both pointed towards the surface; yet I still noticed the oily scum throughout the day. But as soon as I added a HOB or airstone it dissapperead. I currently run an airstone on a timer to go on simultaneously throughout the day and night - no more oily surface. Thus you actually need something that breaks the surface to remove the scum, not just surface movement. HTH


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## upikabu (Sep 2, 2005)

Well, I ran an airstone overnight last night and this morning the surface was crystal clear! :whoo: Fish looks happier too. 

I also pointed the spraybar upwards towards the surface but during the day today I noticed that particles are slowly building up on the surface again. So I think it was definitely the airstone that did the trick. I've put it on a timer so that it will run nightly from now on. I will keep an eye on plant growth and/or appearance of algae and report back if I see problems from running the airstone.

Here are some pics of the tank: 
4 months ago:









Last month:









Today:

















Thanks for all the advice!


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