Advice on Adding a Frag Tank

[Reefried]

I have a 36x18 55 gallon display with a 20 gallon sump, I am planning to add a frag tank set-up in the basement and move the sump down with the frag tank and have all 3 plumbed together. I will be adding about 50 gallons to my water volume. I am looking for thoughts on how exactly to go about this. I can fill it right up with new saltwater and dose calcium, alk, and nitrate to match the current values and add it immediately or should I start the frag tank standing alone and cycle it with liverock like a new tank and once cycled run them all together?

 

[AWarnick]

I think try to match the new saltwater to you existing chemistry and temperature and then start pumping / circulating to the new tank.