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Don't worry about the clowns fighting, they will work it out. The lfs is not giving you good advise though if the tank is cycling with live fish as the ammonia can damage them & shorten their lives with permanent internal damage.
Here the basics of cycling and how many proceed...
add a deli shrimp, let it rot for a week or two...
Start testing and watching... the Ammonia will raise then drop, followed by the Nitrites raising and then dropping, then the Nitrates will soar - once the ammonia & nitrites are gone, then do water changes to reduce nitrates.
Ammonia > Nitrite > Nitrate
Tank Cycled - add cuc, 1st coral, 1st fish or pair (wait a month, to add another fish) fish=bioload
If you don't have one... pick up a sw test kit Aquarium Pharmaceuticals Saltwater Liquid Master Test Kit
Tell us more about your LR & any additives the lfs had you add ... if you want some more input on this... and feel free to ask any questions - we all started right where you are & the great members of RS will help you have success - best tip Go Slow & ask here to verify anything the lfs tells you