This is a downside of canisters; if not set-up properly, you don't get good oxygenation. Having the spray bar disrupt the top of the water does resolve this.
Water can only hold about 8 mg/L of oxygen -- it isn't much, at ideal situations. Warmer water holds less, but this is not really a concern for aquarists. At high temperatures, you're talking about a maximum saturation of 7.5 mg/L, and at low temperatures its 9. Anything else, and the temperature is going to kill your fish first.
With a really low saturation point, you're basically looking at the rate of oxygen being used by organisms in the tank, including your fish and desirable bacteria, as well as undesirable organisms -- everything breathing in the tank. You want the rate of oxygen replenishing to be equal to or greater than the rate of oxygen use.
High pollution in the tank -- lots of organic waste, basically -- encourages the growth of undesirable bacteria (as well as desirable) which will use up oxygen faster. Keeping your tank clean will lower the rate of oxygen usage.
Similarly, anything else that limits the number of organisms that are in the tank will do that. Having less fish, of course, helps.
But, we're not going for "have zero fish." We want to have the maximum number of fish in the tank as possible. So, look at the other side of the equation, how to increase the rate of oxygen replenishment.
Anything that disturbs the surface and creates "splash" will do that. You have your spray bar aimed at the top, and it seems to be breaking the surface. Is that enough? Without buying an expensive oxygen meter, there's no way to know what the exact level of oxygen in your water is. But, are the fish at the surface gasping in the morning? If not, you're probably just fine.
You can add additional pumps or even an air stone to the tank to further add surface disturbance. Note that air stones work by bubbling the surface -- the amount of oxygen they add by dissolving bubbles is negligible, if any.
Photosynthesis is really the only way we can produce oxygen in the aquarium. But, it comes with a big caveat. Plants and algae produce oxygen by photosynthesis; its a by product of, basically, 'eating' CO2. They kinda burp oxygen -- they do NOT exhale it. They still breath in O2 and breath out CO2 (well, respire, they're not really breathing, but... semantics). In good light, there's a net gain of O2 and a net loss of CO2. When there's no light, they can't produce O2, and they use O2 for respiration. As such, plants and algae can actually deplete O2 in an aquarium overnight. You cannot solve a low oxygen problem by "adding plants".
A film on the surface of the tank, or anything that limits the ability of the water to come in contact with the air, will decrease the ability of the water to get new oxygen. Breaking up that film is good. Fats and oils from low quality fish food also cause problems, especially as a canister filter tends to only draw from lower, and leaves surface films.
They make skimmers for canister filters, which do work at breaking up films. I'm not sure I follow what you're planning on doing here otherwise. Just make sure that your canister filter is not drawing in a lot of air, as it can break the syphon and stop it from working.
