My pond was new when I installed my Airmax aeration system but their instructions were very clear for startup in any pond, old or new. 15 mins the first day, 30 mins the second day, 60 mins the third day, etc. If you smell a strong rotten egg smell, dwell at that time until the smell goes away before continuing to increase the time.

[Linked Image]
Be Brave Enough to Suck at Something New!