What test kit should I rely on for K

[duke62]

So I have the Red Sea kit and it is showing my K is at 330. Just picked up a salifert kit and it’s showing my K is at 470. Been dosing potassion-p powder for over a month testing with Red Sea. Now I’m lost lol. This is for a full SPS tank.

 

[Stigigemla]

I have only used Salifert and it is very constant by me. Two times have I raised the potassium level and the calculated dose led to the right result.