Tank is about 3 months old.
Ouch!!
I'm not sure I would have taken any action at all on a tank that new. Nitrates don't really hurt anything and the tank's still breaking in.
Certainly don't add any more fish for a good while until things seem more stable. If you plan to add corals, now would be a good time to start SLOWLY introducing them.
And watch that reactor....do not let it strip the tank.
It's
really out of place on a new tank. If the LFS knew the age of the tank, then you have a right to be suspicious of their advice going forward. (I realize at 50% off it was basically a clearance item....but you didn't need it at all.)
Those nitrates aren't going to last once you have some growth in the tank – and then the tank will be starving (especially corals and algae) just to benefit that reactor once NO3 and PO4 are down to undetectable levels. You should worry about this like you'd worry about calcium and alkalinity getting too low. The downside to this might even be worse, in fact.
Speaking of phosphate, you're also going to need to hawk PO4 as well as nitrates. If PO4 crashes to zero because of the newness of the tank, then you're inviting real pest algae in the form of toxic dino's, cyano or whatever else.
Zero PO4 makes everyone angry that it doesn't outright kill.
I'm sorry to say it, but I would personally shut down the pellet reactor and save it for when you have a bio-load that would be capable of feeding it.