At what degree of salinity would I need to switch over to a saltwater kit? The tank is currently at 0.3%.
I have the API freshwater drop kit and also the Hagen which can do both, but I find the Hagen colours hard to use accurately - particularly the ammonia which is so pale with all those creams. The puffer cannot tolerate ammonia at all so I really want to be on top of it.

I use hagen, it does both, and yes on the color chart with the pale color its really hard to tell, but trust me when the water actually has 0.6 ammonia u can tell, the water will turn a yellow color, and when u compare it to the chart it looks like the 0.6, on the paper its really pale, but u can really tell when it has ammonia, it immediately turns a yellow color