I think what a lot of people wind up doing, is getting what's called a "Power Head" for aquariums.
Look up and read about aquarium filters, canister filters, undergravel filters, and look for people using the term "power head."
All these filters originally ran on air cause air's the cheapest way to move the most water.
But then some people discovered using a water pump and by poking a tiny pin hole in the tube, going out of the water pump, and positioning it accordingly, they make whatcha call a venturi -
What you'd LIKE to make is something called "nanobubbles" and people will peddle you a micro diffuser or whatever they call it, for a premium that is NOT free, but.. it is a real technology.
Something like that but - they're kind of expensive.
Having been for awhile as a kid, in the plants business, and the aquariums business both at the same time, I've seen a lot of people, press a lot of technologies together, to try to multiply their outputs beyond the nature of the science of the times.
Some guys online, have built a new form of Venturi called a CARMIN and I haven't checked how they're made, but a CARMIN - is what a hydroponic grower needs.
Here's a guy who knows one of the best tricks for making a power head: use a water pump and feed the input,
not the output,
These things are an experimenter's delight, and you can clearly see what kind of oxygenation will happen to your reservoir even if you use a very very small water pump, and just feed it a little air, with an aquarium air pump.
When the water is sitting there for several minutes at a time, to several hours at a time, there's not a lot of influx of oxygen consuming entities. You're literally charging the water with oxygen between cycles.
Since your water conditions are almost perfect temp-wise,
at this point you can see for yourself that you're right at the edge of what pythium or some bacteria - I'll bet it's pythium - can stand to live in.
You're right at the edge of driving conditions into those pythium can't make it in.