I really havent encountered large crowds at Seaworld. I go all different times of the year, but mostly the height of the summer in August, and it is always manageable.
Tuesdays are more of a Senior day, with discount tours and things.
Weekends are always more crowded than week days.
IT also depends on when you are going, the time of year.
IF you go during school breaks, like on a 3 day weekend Holidays when the kids are off from school, of course it will be more crowded.
Most of the parks are a lot less crowded from after Labor Day to Halloween, then for that week, it picks up. Thanksgiving again is busy, and then the parks are less crowded until just before Christmas, and its packed to capacity.
When are you going?