OK rnegron. Now I understand what you're trying to do and it makes sense. With the 84F min temp that discus require the water will hold less
O2. Right now your
HOB is probably agitating the surface sufficiently enough to provide for the right gas exchange.
Personally I would hide a small sponge filter (connected to an air pump), in a corner of the tank. This will not only provide enough surface movement, but give you some back up on your bio filtration. Another good tip is to use a sponge prefilter with your eheim. They are easily cleaned and will prevent the impeller from becoming clogged.