Yes, now is a good time to get them.
My experience with Chromis is that they start picking each other off 1 by 1 until there is only one left.
I've tried doing groups of them twice with the same results.
I ordered my CUC from Reefs2go.com. Their price is quite reasonable and with free shipping. Their medium Carribean CUC package is a good starter kit for a 125g tank. LA is also a good place to get them too. You don't need any algae CUC yet. You may later when you see signs of them.
Is this the CUC you are referring to?
http://www.reefs2go.com/product/INV_CARIBCREW-MED/Medium-Caribbean-Crew.html
there is another called medium carrribean package saltwater with more inverts
http://www.reefs2go.com/product/INV_CUC-MEDIUM/Live-Saltwater-Algae-Eating-Crew.html
Did you calibrate your PH probe?