Okay, I think I misspoke. The GB container will be 6" high. I'd like to have about 5.5" of media and about 4.5"-5" of that media being flooded during the cycle. Does that help or do I still need to look for something higher?

I'd like to start with the end in mind so if I would want to grow tilapia to be about 1 pound before harvest, would I be safe with about 15 fingerlings in the 125 gallon tank?

thank you guys so much for your help. I haven't started any of the plumbing so it's not too late to change container size.