I'm going to jump in here and possibly contradict everything everyone in here has said, this is just what I am doing and it may turn to crap but so far so good.
I have a 30G and I run a canister filter. I've had no issues. I don't have a skimmer. My tank has now had water in it for 6 months. Currently have 2 clowns, 2 hermits, to snails and a shrimp. I have just added first corals. Couple of Softies and couple of LPS. So far so good. We will be adding more fish and more coral but admittedly I am going to be very careful about what to keep the load as low as possible.
Does this mean it'll stay good forever, no, am I hoping it will stay OK, yes.
Weekly water changes and bi-weekly filter clean, remove sponges and squeeze them out and swish them in the old tank water from the water change. Is it a bit of a hassle, yes, do I mind it...no.
I run a Fluval 406, has 4 big course filters which leads the water to the bottom basket, bottom basket I then have a layer of medium a layer of fine and a layer of floss. The middle 2 baskets are full of biohome ultimate marine pellets for the bacteria and then the top basket has seachem purigen, fluval phosphate removal pad and then floss on top for a final polish.
The water is crystal clear (I was told the ideal 'look' were the fish look as if they're floating) and my parameters are all stable...for now.
Feeding is kept to a minimum, I.E feed only what the inhabitants will eat, fish, inverts and coral and don't go crazy with it.
Had a green algae outbreak to begin with but that was due to the cycling process with lots of ammonia and lots of nitrates in the water, I let it run its course, it's gone, no potions or messing about.
My 2 Penny's worth, (Cents for you guys), good husbandry is probably the most outstanding and important factor, staying on top of maintenance and treating your tank and water parameters as a whole, taking advice not to chase numbers and keep everything stable.
The one thing I did do, was invest in a RODI system right from the start, I was originally going to go with tap water (Here in the UK and especially where I live the TDS is incredibly low and water standard is much higher/better over the entire country here than unfortunately other parts of the world) but I wanted to do the best I could.
Also I would note, if I went to a bigger tank, I would then have a sump.