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I am using an EcoPlus Commercial 3 air pump in my FT. I am delivering all the air to the bottom of the tank via a length of 1/2" CPVC with a series of small holes drilled in it and weighed down with a leg weight loaded with lead. It is moving the H2O up one side of the tank and down the other, so I get great circulation and plenty of ripple on the surface.

The question is, should I see lots of bubbles and some circulation, or is some bubbles and good circulation preferred?

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I think small bubbles are better for increasing the oxygen content of the water, so lots of bubbles would probably be better.

And I probably wouldn't put lead in the FT. I don't think it will do much harm, but I spent a year working on hazardous material compliance. I'd probably use rocks instead.

I ask about the bubbles because I read somewhere in my research that the surface disturbance is key to aeration, such as on a lake or pond. Just food for thought.

I appreciate your suggestion on the lead weight. My son has a nice size rock I can exchange to hold the air pipe to the floor.

I think the surface area of the interface between water and air is the key, but circulation of the water is important to bring water that has lower oxygen content into contact with the surface or the bubble stream.

An aeration tower works much better and costs less energy than direct aeration of a covered growing medium. Bubbles only create the lift but does add a minimal amount of ambient air to the DWC. Surface area is where aeration takes place and is subject to time, volume, temperature and turbulence.

There has been lots of debate on the topic of where the aeration actually comes from when using air stones in a tank.

Is it from the contact of the surface of the bubbles with the water or is it from the rising bubbles causing circulation in the fish tank bringing the water to the surface to get aerated.

The truth is, aeration comes from both (the exact % of how much aeration comes from which part is up for debate.)  Lots and lots of Smaller bubbles provide more bubble surface to water contact under water while bigger bubbles will cause more disturbance of the surface and in an airlift will move more water.  In the scheme of things in an IBC fish tank for a home system, do the technicalities really make that much different?  (I'll leave others to wrangle that debate.)

Now if you are talking about a raft bed where there is a foam board on the surface then the circulation doesn't really help much in the aeration and you need lots of air stones to spread the aeration out as much as possible so all the plants get some dissolved oxygen.

Air bubbles do practically nothing to increase DO in a depth of less than 14 feet. Gases flow from higher partial pressures to lower.  As depth increases pressure increases therefore it is easy to understand that aeration takes place at the surface where pressures are 14.7psi atmospheric pressure or 1 bar.  Source Emile Gagnan, Jacques Cousteau and NAUI.

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