Okay you have a 55g tank you want to make reef. Well first you need to do lots more reading and Internet searching .... Not to be mean but I can tell by your questions that you need a bit more...
Now with a tank the size of a 55g I would not use hang on the back filters... Not for a (FOWLR
) tank and no way for a REEF.
With smaller tanks you can get away using hang on the back filters.
Now to start a reef I would suggest the following equipment :
unit . U feel is the most important equipment in any saltwater tank.
1- t5 high output light fixture or metal halides or LEDs .
1- 30g or 40g size sump/refugium ......a reugium will help lots in a reef tank....
1- skimmer twice what's rated for your tank .
1-overflow with all the drain/return hoses, and a return pump .
* there are people that use canister filters but I don't know nobody personally lol.
(FYI) with a fowlr
tank you don't need t5 lighting but in reef tanks you do as a minimum. And in reef tank it's best to keep ammonia/nitrite/nitrates/ all at zero! Where in a fowlr
tank it can be more forgiving.