I highly recommend a refractometer. When you get it, check the difference in the reading you get from your hydrometer. Since you have a nano, more care should be taken to keep the correct salinity.
If the LR
was enough (1.5-2Lbs per gallon) and had no die off, from the trip to the LFS
, it could possibly have enough of the beneficial bacteria that converts ammonia to nitrItes to nitrAtes (so this would skip the cycle and be a ready made tank).
Just to be safe, I would put a pinch of fish food in the tank and check for ammonia in about 4 days. If you see any ammonia, you will need to cycle your tank. If you see none, then you are cycled.