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.