korallin 1502S reactor

[ReeferBill]

Ok, so I got a korallin 1502S used, but it seems to be working well. My nitrates are very high. The denitrator has been running for about 5-6 days. The first 2-3 days there was a little amount of gas that was at the top of the reactor. I release the gas every day, but yesterday and today I have had the gas build up so much, that by the time I get home from work(about 8 hours) the gas has built up so much that the pump is sucking air. So there is a good 2-3 inches of gas at the top of the reactor. Is this normal in the cycling of this kind of reactor? Has anyone had this experience?
Thanks,
Bill