I don't keep Discus (my shrimp wouldn't thank me for adding Discus. lol), but I don't use an air pump either, they are too darn noisy! I just make sure that I have enough surface agitation to keep the CO2 levels from getting to high at night, and I use DIY CO2 running 24/7. I do sometimes have to move the suplementary (to my external) Fluval 2 filter higher in my tank to create more agitation, usually after changing the mix in 1 of the 2 bottles as there tends to be a spike in output at first.
Have you considered a small powerhead, perhaps with a venturi, set to come on at night instead? Much quieter and will help with circulation in your tank. They also don't have diaphragms in them that need replacing regularly.
Ade