Welcome to AA
Research is key to successful SW fish keeping and I’d highly recommend reading all the
saltwater articles on this site, the
articles on liveaquaria.com, & picking up a
good book so you have a good understanding of the basics.
SW fish keeping isn’t really that much more complicated then keeping FW or brackish fish. The key thing to understand is that SW fish/inverts come from a very stable environment (the ocean) which has a fairly consistent sg/ph and very low nutrients. They require fairly stable conditions in the aquarium as well to thrive long term hence the reason you want to consider a skimmer which removes DOC therefore keeping your nutrient and no3 levels low. A SW tank can be run successfully without a skimmer (as many have done for years) but require more frequent PWC to keep DOC down. Since SW doesn’t exchange oxygen as well as FW you are also limited in the amount of fish you can keep compared to FW or Brackish. For SW the general rule is 1” of fish per 5 gal. For FW/Brackish it’s 1” per gal. There is virtually no limit on how many inverts you can keep though within reason.
FW & Brackish fish come from less then perfect water conditions most of the time and more oxygen rich environments which make them easier to keep in less then perfect water. If you are keeping an aquarium for the first time and like the colors of SW fish but don’t want the added expense of keeping them then African Cichlids (especially ones from
Lake Malawi) are just as colorful as SW fish. Also since a lot of Cichlids are semi-aggressive as a lot of SW fish can be it helps give you a better understanding of aggression and territorial issues and makes the switch to SW down the road a little easier as well IMO.
If you are still set on going with making your 46 gal tank SW then as zenn mentioned lr and skimmer filtration only (Called the
"Berlin Method") doesn’t require the use of any mechanical filtration ie: sump or hob, but does require water movement through the use of ph. It is easy to maintain although it’s costly to initially setup. You can use a 50/50 mix of
base/lr to reduce costs though and it will serve the same purpose but not look as nice as having all lr.
Also unlike FW or Brackish the use of tap water/de-chlorinator is not recommended due to the high levels of minerals & usually no3/po4. A ro/di unit is recommended for removing all of these elements and to make the water as pure as possible.
A lot of people get them from ebay for around $100. Below are the 3 most popular sites:
Filter-Direct-store (seems to be most popular on this site)
The-Aqua-Safe-Pure-Water-Shop
ROfilterDepot
Also
airwaterice.com is a good place if you don’t want to deal with ebay.