That's ALOT of tank to get ammonia from 6 damsels. the easiest and quickest way is fishless cycling in my opinion. You can dose the whole tank with pure ammonia and go from there. You get to control the ammonia level and you can test each day to keep it replenished up to 4ppm which is a good number I think being that your tank is so large.
How much live rock do you have in there? Did you also add base rock as well?
Typically, the live rock alone can kickstart a cycle if you have enough of it.
180g Reef - 60g Rimless Reef -90G FOWLR- 125g Malawi Cichlids- 40b REEF- 34g Fresh Planted-working on- 20L FOWLR- working on
I have a mix of many different saltwater fish amongst my tanks, but I love my Tangs most of all.