I would not dose anything in a tank this new . It can take upwards of a year to fully stablize out .. Generally you will start to see stability around the 6 month mark however each tank is diffrent .
What salt mix are you using ?
How are you mixing your salt H20
What type of water are you using for top offs and mixing salt water . IE Tap, RO
, or distilled or other ..
Try a aquarium pharma test kit a bit easier to read . When first starting your eyes will not really register the colors but as you do it you will be able to pick up on the subtle colors ..
Also do make sure that it is a salt water test not fresh ... I have done that too , since they sit side by side in the stores :p