How are you handling evaporation? Once the furnace is on in your house you will have more evaporation. You may need to be topping off with more RO water (not seawater).
How are you measuring your specific gravity? (Salinity would never be reported as 1.030). If you are not using a floating hydrometer or a refractometer your measuring devise may not be working properly and giving you spurious readings.
If the readings are accurate. You need to bring the specific gravity down gradually (particularly if there are invertebrates in the tank, fish can have the salinity drop much quicker). I would suggest dropping it down by adding more dilute water as part of your water change or not filling up the tank all the way and adding RO water gradually (perhaps over a week) until the specific gravity got up to where you wanted.