how do I safely add new rock to my

If the rock is fully cured you can safely add it at anytime. If you aren't sure, put it in a separate container of saltwater with a powerhead and test for nitrates, ammonia, nitrites and phosphates. If they check out after a week or so then you are good to go. If not let them cycle in the tub until they are. If phosphates are the only thing that is high you can treat with lanthanum chloride to reduce.

 

Could always go with dry rock snice you already have some live rock from the 29 gallon it will seed the dry rock in the 40. It just depends on if you want live rock or dry rock. But with time will become live rock and is a little cheaper on the pocket book to.

 

I would not add dry rock without testing it first. Some dry rock (like pukani) is notorious for leaching phosphates. Easily remedied before adding but could cause an algae outbreak if added directly to the display tank.

 

If you have an established system and all your parameters are proper then anything that you want to introduce into that system should be quarantined for a week. I recommend getting a small 10 or 20 gallon, a bubbler filter, a small heater, and in the 20 or larger a small powerhead even. Use established water. baseline the parameters run for 3 days, take another set of readings and in 4 more days take the last set... if all is well, water parameters and health of critters then your good to go. If not you can treat whatever you need to right then and there. A quarantine system shouldn't cost you a great deal. Craigslist and here should get you all you need for under 50. Good Luck!