In Florida you need a chiller. Sorry.
I live up in the Pacific Northwest. I had to get a chiller to. My home temp 50 weeks a year is 70 or below and for that time I normally need a heater, but this year the heat wave had my reef at 82F without a chiller, luckily I had a chiller for the seahorses already plumbed in. Without it my seahorse would have been dead.
Seahorses really do best under 74F. I like to keep the tank at 72F so I have a little leway. I'll go down to 68F before the heater comes on. I am keep barbouri.
Even though in the wild they experience temps up to 80F in our little home aquariums (little compared to the ocean if you had an 800g tank it would still be little) the bacteria load is just to great at higher temps IMHO.
For a tank you size you could probably run an ice probe on a controller for not to much money and be completely safe. It works for me.
HTH