I'm sorry, but IMO
, 108W of lighting is not sufficient for a nem in a 55G tank. I know that 55G tanks are very tell more than anything else, and you will need a lot of light.
I had this light fixture:48" 6x54W Nova Extreme PRO T5HO 3x10k/3x460nm Actinics by Current USA*(1081) - AquaCave
Which had approximately 324 watts, and even then, i was still hesitant to buy a nem because that still may have not been enough light, considering 55G tanks are very tall. So 108W on a 55G will not be sufficient for a nem. Whoever that local expert was, was just trying to get you to buy the nem, because your lighting won't support it.
Also, how old is your tank? Nems should not be placed in tanks that are under at least one year of age, because at this age, tank parameters can still fluctuate and nems need the least amount of water fluctuations possible. Your params may be fine at the moment, but maybe a month or two down the road, some little event could happen and alter the parameters, thus putting your nem in even more stress, and nems + stress = tank getting nuked.
I would bring the nem back to where you bought it, get better lighting, and wait until your tank is mature enough to support these creatures.