Rainman that's what I was thinking that the fry might be sucked through the system. A big upside down dome strainer might be a solution. Just thinking out loud for now. The pump has two speeds, one that would really oxygenate the water and the low speed still bubbles the water some. And it may also have a slow flow control. You can tell it's been awhile since I have been in it. The book "Small Scale Aquaculture" has lots of interesting solutions & projects. Getting this a past my wife could be my biggest problem.
