Sounds like a dumb question, but everytime I pump in to fill the livewell on my Puma FTD I will fill it just half way. I try to keep them half full depending on how many fish in livewell to keep weight down. But, when I put on the recirculate or aearator I always com back and check it later and the water is all the way. How do I keep it at a specific level that I want?