I have never heard of the "salt test", can you explain?
Also, I believe it depends on where you live, how often you replace the moss and how often you check on the moisture level of the moss. I have not used the moss here in Missouri during the summer yet because I just switched to it last December. Our home is pretty dry, so if they dump their water I just change it out. No scale rot or any problems so far but I also keep my humidity a tad higher than most at around 70 and everyone is checked on several times a day. Sheds are perfect and they all love to burrow under it, very cute to open a tub and see a little head pop up!
I do believe I may have to do a mix of coconut and moss during the humid months but will wait and see.