Hi Deborah,
My understanding is the buy 1 get 1 day free offer is only available if you buy the tickets online in advance.
If you're planning on visiting Sea World for 2 days, I'd suggest you buy the tickets online in advance through Sea World's website. On the other hand, if you're only planning on visiting for 1 day, I suggest you buy the tickets by other means and make use of discount coupons.
Examples: $5 off Entertainment Book coupon, $10 off discount for AAA members (just show your AAA card at the ticket window and ask for the "special Double the Value $10 offer).
I'm not quite sure what you're asking, so I hope this answers your question somewhat.