How often are you watering and what kind of water are you using (tap/filtered)? Also, why do you fear a buildup of dust? You had mentioned that you had gotten the ventilation figured out, so I doubt dust will be forming. I would stop spraying the leaves and make sure there is a fan pushing air gently over the whole plant. This will prevent dust and move clean air over the entire plant, feeding it healthy O2 and any CO2 that is naturally occurring.