Your tank is still pretty new and the small levels of Nitrite and Nitrate could mean it is still cycling. The Nitrites should be zero and the Nitrates should be below 5ppm. Ideally you should mix RO
water with your salt letting it sit for 24 hours heated with a powerhead to keep it aerated. Then you should test it with a refractometer to make sure your SG
is correct(hydromoters are often innacurrate) Making sure that the water going in your tank is the same temperature and SG
as the water in the tank. I change about 9 gallons of water once per week in my 46g bow which is about 20% water change.
What kind of filtration method are you using for the tank? Do you have any liveRock? If so how long has it been in your tank?