I think a better way would be to do the electrolysis externally, as thechaossmurf is suggesting. That way you could place the aerators in deeper water, allowing for better absorption of the O2 as the water pressure is a factor in amount of absorption. Also, probably at a lower equipment cost.

I was a little surprised at the small amount of increase in DO they were getting, as I thought it would be higher. Although, I am not familiar with the use of pure O2 in that application, so I don't have a reference for my metric.

What I see are fine bubbles of H2 and O2 (assumed) to be rising up and out of the shallow water and escaping into the atmosphere. Not sure why the H2 would not be absorbed along with the O2. The deeper the water the more pressure at the bottom, which translates into more exchange of gas into the water and a longer time to the surface allowing for more contact of the bubbles' surface with the water, and again, more gas exchange.

By the way, a misnomer I detected early on in my Aquaponics learning curve. When the term "surface" is used regarding aeration it does not mean the surface of the water in the fish tank, it means the interface of the surface of the air bubbles with the water they are rising through. So, placing the aerators on the surface of the water in the fish tank is the worst and least effective place you can put them. Even though it may break the surface tension of the surface of the water by placing them at the top of the water, it does little good for adding DO to the water in the tank. For that, you need depth.

You don't need a 6 foot deep fish tank but you do need a tall tower, which can be just a relative large diameter (say 4 to 6 inches) of pipe standing on end with an aerator in the bottom and an air pump capable of pushing air that deep. Just flow the water through the pipe by pumping it into the bottom and letting it overflow out the top and back to the fish tank or directly into the grow beds or wherever. With that configuration, the water coming out the top of the pipe will be super saturated with atmospheric gases, including O2, or just pure O2 as suggested above.

More to chew on,

Oliver