I haven't seen any piping. I'm building a house by the lake and i'm there about 6:30AM almost every day to watch the feeders go off at 7:00. It has been very hot here for an unusually long period of time. The minnows have been hanging out by the bubbles for a long time. Actually, they have been there since just after spring start-up of the system. I'll try to find someone that can test the DO asap. Sounds like a good place to start. Thanks