I have a pair of clowns and a goby/pistol shrimp pair in mine with no issue (had a gramma, but he went belly up during a prolonged power failure
The key is:
1. Don't overfeed. I feed mine every other day.
2. Do 3-4 gallon PWCs *every week*. Do not skip them. Log all of your water parameters before each test so you can see a trend.
3. In the beginning, I tested about every 2-3 days, just to make sure things weren't getting too far out of whack.
4. Top off. Don't let the water drop too much. Salinity and pollutant concentrations will go up quickly. I add about a quart every other day. Use an ATO if you have one.
Make sure you have plenty of circulation (I have 2 Koralia 425s in my tank plus a 150gph HOB
for Purigen), live rock (I've got 20+ lbs) and live sand (I've got 30lbs).