2. Capturing the fry (fingerlings), bring them inside and holding them in a tank that usually has some sort of flow through system bringing in fresh water and flushing wastes & solids.
Bill,
I have now designed a recirculating system for under $500.00 that not only does not require flow through, but it has an external stand pipe that you can pull a gate valve to flush solids out of the tank as many times a day as you wish. This is especially important with small fish that feed constantly and produce a lot of solids.
It's not a typical stand pipe as it is usually empty until the gate valve is pulled which violently fills the stand pipe dislodging and removing any solids in and near the center drain of the circular tank. Of course being a circular tank with centripetal flow the solids automatically collect around and in the center train.
The center drain is only a 3 inch shower drain and 3 inch PVC but the stand pipe is 4 inches. However you only use about 2 gallons of water when you pull the gate valve and then drain out the solids laden water.
It works quite well as the water that fills the stand pipe is not only brown with solids it really stinks! I know it does a great job as a second purge is clear with no odor.
With my larger fish I do a purge of solids twice a day and in conjunction with my clarifer tank of which I clean every three or four days and do a partial water change my water stays crystal clear.
