I would recommend you up your salinity to at least 1.005 and that would be even on the low side in my thoughts. Though I would do it .001 at a weeks time till you get it higher then I would create a recipe that is precise so you come up with the same result all the time for the replacement water.
What I meant by a recipe is something like this.
Personally I run my brackish a bit higher, I have dragon gobie, bumble bee goby and knight goby in it, when I do my water change I add 3/4 lb of salt to a 5g pail then I add 1/3 hot water and use a hand mixer to make sure all salt is dissolved then I managed the cold to get the temp of the new water to match the tank temp. I also use prime to remove bad stuff in the water. I do about a 35% change out on my brackish every 2 weeks or so.
here is a link to a site on mudskippers for you
http://homepage.mac.com/nmonks/Projects/FAQ/5c.html