HOW TO SET UP A TANK, condensed verions (retitled)

1. if you're going to have corals you need to aim at having either an all-in-one tank---or a sump, skimmer, and good lighting. Your rock and sand take the place of a filter.
a. stony coral and clams: need brighter light, good circulation. For sps (colored sticks) you need high flow and a super skimmer.
b. 'soft' coral is more forgiving, can exist without a skimmer if you don't push it, but it's a good idea to have one.

2. if you're fish-only you can get by with a filter: you have to change it meticulously. Rock and sand will help it out, but are never as strong in the presence of a filter (up and down of food supply as it's cleaned and not) as without one. Still, with big messy eaters, you may need that filter. Putting a little mushroom rock in your tank is still a good idea: spread-out mushrooms are an indicator of good water quality. Shriveled mushrooms are an indicator of trouble---far ahead of when your fish will announce it by showing distress. Gives you a heads-up visual test and helps.

3. TO START: get aragonite substrate, 1 lb per gallon. Dry is as effective as 'live sand'. It all gets live eventually. I prefer medium grade, which does not blow about in a strong current: not as pretty as 'fine,' but in a high-flow tank, it stays put. Do not get crushed shell or coral---it has problems. I lay down eggcrate [lighting grid: Lowes] on the bottom to prevent rocks rolling.
a) rock: you need SOME live rock. about 10% live at 1-2 lbs per gallon. Choose really lacy, holey rock. Limestone. Dry rock will turn live. Takes about 12 weeks to cycle as opposed to 4 with all live rock, but will save you enough to afford better lights.
b) wash the sand before using it. Rock goes down first, then sand, then live rock if you only have a little.
c) use ro/di to mix salt with---usually 1/2 cup salt mix per gallon of fresh water. This yields a salinity of 1.024. Keep it there while you cycle: draw a 'fill line' on your sump or tank representing perfect salinity, and 'top off' with fresh ro/di as it evaporates.
d) marine tanks don't have lids as a rule. But a jump screen is a good idea once you get fish. Most will go airborne if frightened. You WANT that evaporation to go on, and the cooling that results. There are so many pumps and bright lights, heat is your enemy.
e) keep your temperature about 80, day and night. This is another reason to have no lid. It's a good thing to run your lights and everything BUT the skimmer, which just has nothing to skim until you have fish.
f) plan a quarantine tank: no rock, sand, no cycle, just bare glass and water and a heater, not even a light. Keep all new fish there for 4 weeks to be sure they don't bring in 'fleas'. Parasites are not nuisances in this hobby: they kill, and they get into your sandbed and reproduce and infest every fish you own. Quarantine is serious business. You can start a fish in qt 4 weeks before you expect your tank to be ready.
g) don't get 'miracle potions' of bacteria and for gosh sake, don't get a fish. You're good just with the natural dieoff from your rock, but if you just have to do something proactive, drop 4 flakes of fishfood in a day until you spot ammonia in your daily tests. Keep feeding imaginary fish daily---and 5 days after you fail to provoke ammonia, you are cycled.
h) expect sheets and waves of green hair algae. Phosphate is the cause, and rock and sand come in with a load of it. So does conditioned tapwater, which is why we suggest, nay, plead with you to use ro or ro/di water. You can get ro from your supermarket kiosk. Owning your own ro/di filter is a Good Idea, and you reach the breakeven point in about a year for a 50 gallon tank.
i) btw, the optimum tank size is 50-100 gallons for a beginner. The smaller or the larger the tank, the bigger the problems. For little tanks, it's like driving a sports car---every twitch produces a huge, often bad, result. For big tanks---everything is huge, heavy, and spendy, and water changes are (at 10% per week) both spendy and heavy to lift. The 50-100 tanks are middle of the road, let you keep blennies and gobies (50) or some tangs (100). Be sure, however, if the big fish (tangs and angels) are your love, you spring for the big and Lonnnnnnnnnnng tank. These are swimmers, high speed, and they need it, the way you can't keep a race horse in a little pen.
j) read the sticky on acclimation: a refractometer is a very good investment---it saves fish. If you are within .002 salinity, between the fish's bag and your qt tank, you don't drip acclimate: just put them in---and if you've prepared by finding out the salinity the fish's bag will be---you can prepare that tank so there is NO drip acclimation---which can kill. The explanation is in that sticky.
k)don't dose any chemical you don't have a test for.
l) if you have a salinity accident, correct it slowly, no more than .002 per hour. Topping off with salt water is a good way to raise it, just in the natural evaporation.
m) never trust a heater or thermometer. Use 2 thermometers, and touch the glass often in passing, just to be sure.
n) clowns are interesting fish, but they are aggressive---some more than others. The redder, the more so. And you should NOT get an anemone until your tank is about a year mature. Give your clowns a nice hardy coral to wallow in and they'll be quite as happy. Anemones are difficult, delicate, and in the hands of a new hobbyist, downright dangerous to the rest of the tank.

Most of all-----come here and ask BEFORE you do something, and NEVER impulse-buy a fish or invert. It mostly ends badly, and sometimes takes out a tank in the process. There's nothing your fish store gets that they won't get again, especially if you ask. Don't buy 'rare' things: translation: it usually doesn't thrive and often dies. Don't buy exotic fish. Same reason. These aren't decorator items. Get tough little guys that eat plain food and can put up with a few beginner mistakes. Leave room in your tank for them to grow. Many fish we keep reach a foot in length: know how big your fish will grow, and pick what will be happy in your tank.

Good luck---and always ask. There's a 'why' for all of this. It's better to know one sure way that works and get experience at this---and then you can try new theories. Don't get in a hurry, don't take chances, and don't shortcut. If there were a faster way, I assure you, everybody would do it. This is a hobby that's been around for more than a hundred years, and people have tried almost everything, finding many things that don't work. We've sifted out the things that do work, and if you can just get through your first year, you'll find this all makes basic good sense.