For the hydrometer...I usually submerse them a couple of times just to get it ready. Empty all of the water out and then slowly put the bottom of it into the water and continue to push it straight down into the water. Slow...really slow, is the key. The water will go in. You want it to fill slowly and not get bubbles on the little needle/arm. Fill it all the way, take it out and put it on a level surface. Wherever the needle ends up pointing is where your salinity is.
There is such a thing as a refractometer. They are very accurate. Hydrometers tend to be off, either reading too high or too low, which can be really bad in a reef and not so good on a FOWLR
For shrimp...one or two, fresh not frozen, I've taken the shell off...not sure that matters. It was interesting asking the guy at the meat counter for two shrimp. He did not believe me and I finally had to explain that I was dead serious and what I was using them for.