Bill, perfect description of a Hypo system.
Because the hypo water is so low in oxygen, it has a desire to off-gas the hydrogen sulfide and carbon dioxide gases and absorb oxygen. The vent tube allows the off gas and at the top there is usually a stair case type aparatus for the water to trickle down and gravity feed back to the bottom.
Another type of hypo system would be to have a pump on shore pulling water into an oxygen cone from the top. An oxygen generator would be pumping pure O2 in the bottom of the cone. As the water falls down inside the cone, it mixes with the pure oxygen and gravity feeds back to the hypo at a super saturated level of about 20-30 ppm.
Just an invention while sipping my JD.
