Okay, since no one else seems to want to play:
pH meter (waaay more accurate than hobby level chemical test kit)
Refractometer (leave the swing arm hydrometer to the FO crowd)
Salt (most of the major name brand salts are okay)
RO-DI source - either an RO-DI system or an LFS that sells RO-DI water. Second choice would be grocery store filtered water if it is RO.
An accurate thermometer. Floating glass is not a good idea because with high flow, they might get broken in the tank, unless you get one with a good suction cup to keep it still.
Test kits - ammonia, nitrate, nitrite, calcium and alkalinity test kits (from what I read I wouldn't get a phosphate kit because they can't really measure down to the levels you hope to have in a reef tank - if you have algae problems past the normal cycle most LFSs will test for you) Salifert seems to be a popular brand, but I don't actually have water in my tank yet, so I have never played with them.
Grounding probe - cheap insurance for you and your critters against stray voltage shocks.
Heater(s) - again most of the big names work fine. If you will have a sump, it's better 2 small ones than one big one, although for a 20 you might not be able to find a small enough heater. The idea behind 2 is if one fails your tank won't get too cold and if one sticks in the on position half the watts means twice as long for you to catch it before it cooks your tank. If no sump, try to find an unbreakable, fully submersible heater so rockslides don't smash it.
Lights / Flow / Filtration will depend somewhat on exactly what you want to keep. Softies requrie less light / flow in general than SPS (fuzzy sticks). If you want SPS and clams you almost can't have too much light. Same on filtration. Softies and LPS you can get by with live rock / sand / weekly water changes. Lots of fish or you want SPS, then you need to start looking for a skimmer. Depending on weather you plan on having a sump or not decides alot on skimmer choice. If you have a sump, plumbing is more complex and you will have to have a return pump, but you get some of the junk (like heaters and some power heads) out of your tank.
Was hoping some of the more experienced folks would dive in here. I have been studying for a couple of YEARS between here and some other sites, but I am moving very slowly for a variety of reasons. Hopefully I will have water by Father's Day. That being said, I am on this and other sites pretty much daily and have several books under my belt. It's no replacement for experience, but I will share what I have read. Most of all, I encourage you to study alot and go slow. I think alot of the folks that quit in the first 6 months or so might have been saved by some patience and research before they threw down a big chunk of change for stuff they didn't understand.
As you can see, $400 is going to be a challenge, and you can bet that you will quickly surpass that number if not in the initial set up, then probably within a year. It's hard to nail anyone down for what you will spend (I think most don't want to think about it) but I have seen estimates between $15 and $40 per gallon to set up and around $1-2 per gallon per month to feed / power / maintain (some estimate higher). Alot of that is determined by what you plan to keep and how do-it-yourself oriented you are.
Hopefully wiser voices will be heard, but I figured I would at least throw in my two cents. Good luck. :beer:
