There isn’t anything in a tank that will hold on to or release salt. Unless of course you add undissolved salt. Adding and consuming a significant amount of 2-part Alk/Ca will increase salt. Another common reason is if top-off from evaporation is with saltwater instead of freshwater.
I’d start by bringing some of your water in to Kenny’s store and have him check the salinity. Bring your meter or whatever you are using to check against his at the same time. Salinity can be difficult to know the ground-truth, but you should consider Kenny’s readings accurate.
Next, if you’ve confirmed your salinity is high, the solution is simple. Dump out some water and replace it with the same amount of fresh RO/DI water. How much depends on the size of your tank, go slow at first. Re-measure. Repeat. How rapidly you can change is open for debate, but if your reading is accurate (1.030) and you want to get to 1.026, you can probably get there in 1 day safely with a bunch of small corrections.
Consider using salinity in ppt or PSU, either of which would have a target of 35. Whole numbers are easier to not make mistakes with. Instead of specific gravity (1.026).