My advice to convert your tank from fw to sw is this.
Remove all the stuff you don't want to kill, leave the rest. Then take a hand mixer and measure out 1.5 lb of salt for each 5g of water you will have in this tank and get mixing. Convert that puppy over, then pack on that new equipement and do the needed testing and wc till you get the readings good and then throw in a couple of cheap test pilots like some chromis and in a month or so your tank should be good to start. Depends how long the bacteria takes to set up with your new tank, but I have converted a fw to sw in this way, though I kept the same filters and stuff more than a few wc in the process though. I still have the fish I did this to in my 180g tank right now 2 years later.