i agree...it's generally called being stupid by posting useless information as well.
agreed that the OP will need a bigger tank, but if it is a Florida gar you will be fine with a 120g wide, which is a 4' x 2' x 2' tank. this gives you the width of a 180g, but not the length in case you are presently constrained by space (or even cost). FL gars will rarely get up to 24" in captivity, and even getting close to that will take at least a year or two from now given his present size.
as for tankmates, both the oscar and RD should go. if not, then find them a different tank. these cichlids are too aggressive to keep with gars and will likely eventually kill it either by attacking it or spooking the gar into breaking its back.
hope that info helps, good luck--
--solomon