Archers don't need much salt if any to thrive. 1.004 SG should be fine for them.
This isn't quite accurate information.
The first thing you need to do is properly and accurately identify which species of archerfish you have. I have never seen a LFS classify any archerfish as anything other than T. jaculatrix which is commonly in correct. I have found through personal experience, and read in books, that T. microlepis is usually available more often than T. jaculatrix and sold under the wrong name. Unfortunetly images on the internet and some books are usually mis-tagged as well. The publication "Aqualog Special: Brackish-water fishes" has accurate ID photos. If you're not sure you can post a pic and I'll ID your archers for you.
There are 3 species in the Toxotidae family that are commonly available in the fish trade, here are the species and SG they should be kept at:
Toxotes microlepis - up to 1.005
Toxotes jaculatrix - 1.010 to 1.015
Toxotes chatareus - 1.010
If you have T. microlepis you'll be ok in lower salinities. As you can see, T. jaculatrix and T. chatareus require at least half seawater. T. jaculatrix is also the only member of the archerfish family that is found on the Solomon Islands, it's believed they swim across the ocean to get there. My T. jaculatrix have spent short periods of time in full marine. Most brackish fish actually do better in conditions with fluxuating salinity. In nature the salinity in their enviornment changes a couple times a day. In the home aquarium this can't be performed because our biological filter will die under such drastic changes.
On a side note the strictly freshwater species of Archerfish, T. lorenzi, and the mainly freshwater species, T. blythi are not avaliable on the aquarium trade so all archers at your LFS should be treated as brackish unless otherwise identified.
Hope this helps.
