Measuring salinity:

http://westernfarmpress.com/irrigation/measuring-salinity-irrigation-water

Also, if you go to ebay and search for "salinity tester" it will come up with (at this time) 83 active listings. I don't know which one is best.

www.hoosierpondpros.com

[Linked Image from lh6.ggpht.com]
http://www.pondboss.com/subscribe.asp?c=4
3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).