You can use the 50/50 you already have, just add some distilled water to it, to make it close to 30/70
Especially in south florida where it doesn't get that cold I know a lot of people use just straight distilled water in their systems, antifreeze doesn't affect the boiling point too much, I have put a higher pressure radiator cap (off of a 300zx) and that has lowered my temps during the summer pretty good