I can't begin to tell you how important both a RODI
unit and a refractometer are.
A refractometer tell you the SG
of your tank water and your PWC
water (teh partcial water change you do weekly). There is no liquid test for that.
You need to test your water at least weekly for the first year. That's why it's so important to have quality test kits on hand.
Should you ever have a problem and and post a question here the first questions will be:
Please post the following info:
Do you add any chemicals to the tank? (ie. Buffers or Supplements)
What do you feed the tank? (Frozen, Flake or Pellet) How often do you feed?
What kind of Salt Mix do you use? Do you let it sit for 24hrs with a powerhead and heater to airate and mix fully?
Do you use RO
water? How do you Top Off evaporated water?
The more information you can provide the faster we can formulate an opinion on what the problem and cure are.
Take your time and all should be fine.