I don't think there can possibly be enough O2/N2 accumulation as to cause a 24" reactor at 1 bubble CO2 per second to constantly burp tiny bubbles. While it is normal for a reactor to burp bubbles during the first few days of operation, if it continues to burp tiny bubbles then your flow rate is stronger than the natural buoyancy of the CO2 bubbles, thus flushing them out of the reactor. Two things you can do to remedy this: (1) lower flow rate and/or (2) put more bio-balls, bio-rings, etc. The former is usually not very negotiable but it is pretty easy to stuff the reactor with more bio-balls/rings/stars/etc., even when it has already been sealed. Simply hack-saw the PVC tube in half, stuff it, and join the two pieces back together with an appropriately-sized PVC coupling. These obstructions slow down flow rate and trap gas bubbles; thereby allowing their dissolution before being blasted into your tank.