Thanks for the info! The tank he's in is a 90 with three tinfoil barbs and a Pleco and I've had them in this tank only for several months now. The Oscar is about a year old now. I worried that my water perameters might be askew but every time he turns bright yellow and I test the water everthing is fine. I'm happy to hear your comments, Zach, because that's excactly how mine behaves and I'm glad that it's normal! Thanks again.