I would recommend buying some test kits and get a grasp on your parameters and how to tell there is a problem without having to visit the fish store.
Example, salinity, ph, temp, alk, cal, mag, nitrate and phosphate should be the basic kits you have at home. I would recommend salifert.
Are you using RO DI for top off and salt mixing?
What is your salinity at?
How are you checking?
