First Saltwater Tank, 60G

Every time you add a fish, you have to let the tank and good bacteria adjust to the new ammonia that will be present. Since you already have fish in, I would do a 15% water change every week until the nitrates are 0. Then 10% a week after that. You should be ok, just don't add anything else until your levels are down. Also make sure to use RO/DI water. Most LFS will have it for a cheap price per gallon, to do top off and water changes.
Also, When you top off you tank, just add fresh RO/DI water. When you do your water change, then you mix up saltwater.

 

I was also wondering about topping off.
Some of the local shops say, "Just use some tap water"

So if I were going to use RO/DI water to top-off, would I be able to just keep a 5 gallon jug of RO/DI water?
Or would I need to do something with the water, like a power-head, etc?

Or can it just sit somewhere as is?

 

The top off water needs to be ro/di water, tap is a big no no for sw tanks.

It can cause huge algae problems on top of all the chemicals and extra elements it can add to a tank. Protect your investment.

I make up my saltwater, swish it around some, let sit over night and give it another good swish and it is fine. A power head for movement would be fine though.

Stocking for saltwater is very different than fresh. Longer between additions, values of 0 for ammonia and nitrites only. Saltwater tanks do much much better with a smaller bioload fish wise.

Congradulations on the new tank it looks great.

 

Today I found about 3 white starfish that must have "hitch-hiked" their way here on the live-rock.
Pretty cool.