This question goes to the people who has a saltwater aquarium thank you?

i bought a 55 gallon tank. no ro/di no live rock yet. and i have the right light. i got the filter and heater that about it that install to my tank. i measured the gravity and salt and it ok. Now the tank been set up for about 1 week. so i decied to add 2 damsel in. but all of the sudden the scale flare and there color fades away sometime. tell me what wrong with it am i missing something important? if i do a 20% water change do i need to add salt to my new water that im going to put in or not. if you cant answer this question im thinking a sample of water to petco to mesure the nitrate nitrite and more. thank you for trying.