I have a Aquarium Pharm master test kit for FW. My tank is at 1.016 SG. Can I use this kit or do I have to go spend another $30 and get the SW one? Whats the difference anyway?
The only different test I use from that kit is the SW ammonia. Everything else works the same in SW. If you're going to keep a reef, that's a different story.
If you want to be safe and not risk the fish you'll later put on, I'd suggest getting a SW one. There are plenty kits that work very well for a lot less than $30 if price is of concern. If you were looking to browse around, there's a highly recommended one at aquariumguys.com that's about $14.