Ah, that's what I forgot. There was something about the wood stones that I didn't like. And a strong pump doesn't mean the volume, has to have the pressure, and there is not a lot of pumps today that are good enough. Years ago there was a pump that was a 2 wheel design with a belt that worked great for air stones. Doubt they make it anymore. name escapes me, like a steam driven locomotive. Second best was a luft pump, but don't believe they are the same quality as they were years ago.