So I had this issue with shipping corals, I would continually use my own water to fill bags of corals for shipping, thinking that when the top off unit would activate there really would not be a huge difference in salinity. Boy ways I wrong. After doing several shipments I decided to check my salinity with a common refractormeter.

Let me first start off by saying that you shoudl regulary calibrate your refractometer often, well I didnt and thinking I was right on with my water changes, come to find out that I was actually about off, by alot. Once I calibrated my meter I wanted a safe solution to monitor my salinity with a quick visual check. So I purchased the PINPOINT® Salinity Monitor hoping this would help.

I have just recently this up so right now everything seems to be working. The monitor does not give you salinity it give you conectivity, that is fine as long as you know your numbers. 53 is the number I am hitting. 

Pin Point Salinity User Manual