Here's my 2 cents!
You should never add a fish to your display tank without first quarantining.
And you should definately get yourself a refractometer. Those swing arm thingys are not very reliable if at all!
All LFS's have a huge array of diseases and parasites and even if the fish is supposed to be disease resistant you risk introducing whatever to your tank.
Quarantining needs not be expensive, all you need is:
Properly sized bare-bottomed tank $10.00 - $20.00
Heater $15.00
Simple Sponge Filter $5.00 and pump $10.00
Cleaned PVC piping or plastic decorations so fish can hide Free at a plumber
A place to put this QT
Generally this is cheaper the the cost of the fish you'll be buying so it's not worth playing Russian Roulette with your fish
