How crowded is it normally? Would I be better off buying the ticket online than in person?

If suggest buying online. It's not worth the risk of it being busy.

If you go just when they open on the weekends there will be no lines for tickets and the aquarium itself won't be crowded at all. By 11 or so it can get quite crowded, depending on the weather.

If you plan on going more then once become a member. Totally worth it. I take the kids once a month.

Yes...the lines for purchasing tickets can get long n you have to stand outside..

It really does depend on the season. I got mine online, but the day I went there were no lines at all.

Online. Weekends are very busy.

Depends on the time of day and the weather. We went on a rainy day two hours before they closed and didn't wait in line. This was also on Friday if School break week.