Worried about 'dead zones'

Hi! I recently switched to a canister filter and got rid of a small cascade filter that was on the left part of the tank. This is a 10 gallon planted aquarium; with heater; fully cicled (0 NH4/NO2/NO3) and I add 1 ml of flourish general fertilizer weekly.

Now I notice much less water disturbance at the surface of the left side of the tank. Given the current stock (3 harlequin rasboras; 5 neon tetra; 5 ember tetra; 1 apple snail; 2 nerite snails; ~10 cherry shrimp) and the amount of plants in the tank (see video); should I think of putting an airstone in the opposite corner of the sponge filter? I worry that at night plants and fish will start to compete for oxygen.

Any thoughts/feedback are greatly appreciated