Salinity dropping why?

[swill]

I have a 7 gallon fluvial tank with A singel seahorse in it live sand and a couple of fake plants. My salinity seems to drop for some reason. I had mixed the water 1.022 and then checked about a week after putting the seahorse in and it was down to 1.014. Some how the seahorse surveyed. Does anyone know why this is happening and how did my seahorse survive