A hydrometer only tells you if you have the proper SG
. You need to be testing for Ammonia, NitrItes, NitrAtes, PH ect. The fact that the fish are small now doesn't matter they will grow.
I don't agree with what your LFS
said. Adding one piece a month til you get to 25-28 pounds still isn't enough IMO
. 1.5 to 2lbs per gallon is the general rule for good filtration. Which means you need at least 35lbs total in your tank to keep up with filtration.
Inverts aren't going to keep things balanced. 1" of mature fully grown fish per 5 gallons. The cleaner wrasse (I'm assuming it is black and blue) will most likely not survive in your tank or any other for that matter. It feeds almost entirely on parasites found on other fish. It is a fish best left in the ocean.
When did you put the first fish in the tank? How long had it been running before you put that fish in there? Have you tested your ammonia levels? Have you tested for anything other then SG
(your hydrometer)? Have you done any water changes yet? What kind of water are you using to top off after evaporation?
Welcome to AA by the way!