Hey Brian I received your message with questions about spawning tilapia. I apologize that I have not returned your call. We are all learning from your project, and I feel this thread is an appropriate place to discuss.
I think first of all, you would need to define your program. Back to basics...what are your goals? Looks to me like you have set up a RAS production system capable of overwintering. With your overwintering system, your goal could be to hold and grow fish produced from a prior season so that you may stock em in your lake when the time is right in the spring. With this program you may be able to produce and/or hold up to 1/2 lb of fish per gallon of water.
A tilapia hatchery spawning setup is intensive and involves few fish: only one stud male, several females. Normally the tilapia will spawn without any help or special nesting material. Give the females a place to hide, and they will find cover once they have a clutch of fertilized eggs to protect. A short 8-10" section of 4" PVC pipe, capped on one end, is a good tool. If you can determine that you have a female fish in the pipe, simply trap the female by capping the open end, and move her to a separate tank or flush the eggs from her mouth and hatch them in specialized hatching jars. If you have a side view of your fish, you can identify broody females by their bulging mouths, but if you have a top view then you can't see this. Once you have successful fry production then it's game on, starting with fry powder and working up to pellets. Fry survival is critical in the captive tilapia hatching game.
From my perspective, your setup is best suited for pond tilapia production through the spring/summer, then harvest and stock your indoor system in the fall, overwinter them, and stock em in your lake in the spring...
