I always hated using moss. To me it has a funky smell when you get it damp. I've used ReptiChips and now Eco Earth again and both don't smell like fish. They have a dirt/earthy scent to them. You shouldn't be smelling the urate as the coco husk should have broke down the smell. How old is the stuff? Maybe it's soaked up it can to break down. And I've never heard of a BP musking. I keep all my cages around 80-85% humidity. Now when I used paper towels for Caesar my retic, you could really smell his piss as paper towels don't do anything for the smell lol but it didn't smell fishy, just kind of a bitter 'snake piss' smell haha. I've kept snakes for a long time so to me, the smell is just 'snake piss' smell to me.