DETECTIVE WORK: chain reactions you'd never believe...
1. case one: fish turns up with red mark on side. Disease suspected.
A: possibly so, but in one case of this, the red mark was from a pistol shrimp. How detected? The wounded fish dens in burrows and low in the rocks at night. More than one fish turned up like this. Fatally so. Removing the pistol shrimp prevented further cases.

2. case two: another red mark, but no pistol present.
A: The offender turned out...

...and it's useful to know these aren't magical rituals, but processes with purpose.

1. Cycling. 2+2=4 with most critters, but with bacteria, 1=2. They divide and multiply under favorable conditions, and fortunately their 'favorable' is pretty broad. To hasten cycling a wee bit, keep your tank temperature a steady 78 degrees and keep the water circulating to move the water around. You can 'ghost-feed' your tank a few flakes of flake food a day, which will supply any nutrient NOT provided...

Canister or sump/skimmer? how to decide.
Modern canister filters can cost as much as a large sump---
They ARE good: but their goodness mostly has application to fish-only setups. This isn't to say you couldn't run a softie tank with one---we ran a nice little softie/small fish tank in a 30 long with a Penguin filter, no sump. It had algae; but hey, it was healthy.
To run a fish-only, even with a monster filter, you're going to need to do filter-cleaning: to run a sump, nope,...

1. FOR A FISH: Ask your dealer what his Salinity is, and set your quarantine tank to that, precisely. The minute you open your bag, test the water to be sure he's right, and that you are, within .001 of a salinity-match; and a quick ph check is not a bad thing either---(if your ph should be bad (remember bag-water ph starts shifting the second the bag is opened) or if the salinity is not what you were told it was, a drip acclimation may be your only resort, especially if you have an especially fragile...

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:...