August last year and compared to other months during the summer that I have heard about (and even in first of August when I visited several times previously), the crowd tends to be just slightly smaller at this time when we were there presumably due to the end of summer wrapping up and very close to most schools starting to open.
We went to all the shows and attractions with no hassles; major crowding was not a problem at all.
However, Friday is reported as one of the busiest days at Sea World so from that aspect you can expect a sizeable crowd on that day.
But, I would think it will still be much more manageable in relation to any other earlier summer month whether June or July when you would really be in the thick of people no matter what because of the heart of summer vacation.
So, I believe you are definitely going at an overall excellent period during the summer when atleast there won't be as many present as during early-mid summer (even though you will still run into a crowd) and find Sea World worth the time spent also.
Hope this helps.