I guess I should chime in, since I've had a planted / FW
aquarium for many years, and am currently still buying everything for my SW
setup. I just finally sold my prized $700 giant red finned gourami (FW
), and cleaned the aquarium out.
The primary thing is, a lot of your FW
setup you will not longer be able to use, pretty much everything inside the aquarium, even the media inside your filter shoud be changed. I picked up a Reverse Osmosis water filter this time around, and a new sump/filter/skimmer (which is NOT a necessity, but will make life a little easier, primarily in the form of less partial water changes required.).
I think the best way to start is with a FOWLR
setup, and in a year or so you can begin to introduce corals to make your reef aquarium. The other thing to keep in mind is the length of the aquarium is key, SW
fish like a lot more swimming room... so if you're going to take down your 55g, maybe check the local classifieds and invest in a used 100+ gallon, you can always use your 55g as a sump, fuge, or sell it.
Keep in mind, the cost adds up quickly... yes live rock is key, but consider the price of live rock... at around $4-$7 a lb, and considering you'll need around 100lb with your current setup, that's $400-$700 in rock alone. Live rock is called live rock because of the benefical bacteria growing all over (and in) it, so you can cheap-out and buy half "dead rock" (once live, but kept out of water usualy.. nothing left living on it), and half live.. and in time, the organisms will populate your dead rock and make it "live rock" as well.
Other things to consider are lighting for a reef tank, power heads required, and argonite substrate.
My top recommendation (what I did) is check your local classifieds, there are ALWAYS people in the area who are tearing down their SW
setup, and you can purchase everything you need second hand and save around 50-80% easily. A lot of things they'll even give away. Even live rock sells for around $2-$3 from the hobbyist who's closing up shop.
So this may be an option for you as well. Other than that, the fish are obviously more expensive, and you can't have as many 'fish' in the tank as with SW
at one time, however you can make up for that with other little critters roaming around... (starfish, urchins, snails, crabs, shrimp, etc.)
Hope this helps..