Adding Corals
 

What is the general rule for adding corals to a tank in terms of how long the tank has been running? I've had mine running since the beginning of February and have been thinking about maybe adding some.

If you've got the hang of maintaining levels, go for it. Start slow, see how they do.

What are some good types to start out with?

Well that all depends on your tank. Size, flow, lighting. Give some details, we can suggest some types.

Along with Brad's questions, what are the readings of everything you can test for (include salinity and temp)? Do you have coralline growing on your glass yet?

20 gallon tank, Fluval 305 cannister with spraybar outflow, one Top-Fin 50 powerhead, Coralife 65 skimmer, Coralife 24" 65 watt 50/50 fixture (2 white, 2 actinic 03 blue), salinity usually in the 1.023-1.025 range and temp about 26-27 celcius(80F).

I forgot to add...plenty of coralline growing on the live rocks.

You should try to keep your salinity a tad more stable. Try topping up twice a day. :)

Has the coralline spread to your glass yet? Personally, I don't like to add corals until there is quarter-sized patches of coralline growing on the glass which indicates the tank is "settling in".

You didn't mention anything about your parameters... pH, Ammonia, Nitrite, Nitrate, Calcium, Alkalinity, Phosphate, etc.

Feb you should be good to add some mushrooms especially if you have coralline growing. Start with those they are hardy. Then maybe a leather.
Drop the canister in my opinion they cause more trouble than the are worth. Or at least take out the sponge.

Why is the cannister trouble?