I had hermit crabs for years; the thing to remember is they have gills so a humid environment is a must.
When you provide a fresh water dish and a saltwater dish they will go back and forth between the dishes to balance their salinity needs (so measuring the amount of ocean salt you're adding isn't necessary).
I'm not sure I'm familiar with the product you are talking about...is it a saltwater fish tank water conditioner? That removes heavy metals and chlorine? Or is it saltwater-tank-ready water?
I used to buy the Marineland box of straight ocean tank salt (the box says on the front it contains enough for 10 gallons) and every time I changed their saltwater I would add a new pinch of salt. The box is white and purply-maroon. Petco and PetSmart carry it with their fish stuff.
One thing I had in my environment for them was a submersible filter (i.e for turtles). It created a water fall effect and lots of water movement if you have your tank divided for water, rather than dishes.
Are you providing a heating pad? Temperature is also very important!
I have pictures somewhere I can post tomorrow.
What kind of hermit crabs do you have? It doesn't matter as far as salinity needs, but I was curious. I always favored Ecuadorians (red claws) over Caribbeans (purple claw) and Strawberries (white-spotted, red claws). Though Caribbeans move shells a lot more often, which is fun to watch.
I think you're doing the right thing asking for help with them! A lot of people consider them disposable pets and it makes me so sad.
:thumbup
