I don’t know that there is anything wrong with Red Sea tests. Lots of people here like Hanna checkers, but that’s only because they spit out a handy number, you don’t have to interpret anything. That DOESN’T mean they’re more accurate though, just easier. FWIW, my previous career was a chemist (now an ER nurse), so I’m very confident performing water testing. Ironically, I don’t do it often enough, because I’m lazy. Personally I use Salifert tests. Much cheaper than Hanna, and accurate.