I only use Salifert anymore. API are lousy. I had a Seachem Alk kit that had bad reagents (and the mfg admitted this). After spending $$ chasing non-existent problems, I swore off of anything but Salifert.
In any case, the KEY thing is age. Reagents do not last long, and my belief is that kits over a year old are suspect. Fresh reagents are key to valid results. BTW sunlight (or tank light) is very hard on them. Since many sit on the shelf for that long before being sold...
215g FOWLR... and anemones, GSP, gorgonians... carp, that isn't FO!
"I killed my first SW Fish in 1971..."