well if you dont see the fish for a few days you would pull its up and check but if you had a pair of fish that were acting a bit funny i wouldn't check for a few more days just incase they were breeding
My lfs suggested pvc for tunnels but my hubby wanted something clear. His solution- glass hurricane shade(as in candle holder). My nics and pacus seem to love it. They used to fight over my caves all the time. I just hope they don't break it...