The hobby grade test kits are not very accurate..
I have found red sea test kits to be pretty close to each other from batch to batch and stability is the main thing. The worst is Salifert, I have tested one kit to the next and some are so off from one another they can nuke a tank...
I now test with red seas and back up a a second test with a Hanna checker.
Question is which on is actually right.. I have wnet for stability from batch to batch....
I like API for Calcium and Alkalinity as long as you ditch the vials and get a 5 ml syringe. They're really easy to use, and as accurate as any others on the market. Being easy to use trumps a little resolution when it comes to alkalinity, plus no one needs more than .5 dKH resolution unless you're trying to dial in a CA reactor quickly.
Magnesium, I prefer Salifert. Salifert Nitrate and Red Sea nitrate are both good choices. For PO4 the Hanna checker is about the only somewhat economical choice. Other PO4 test kits are pretty worthless and don't have the resolution we need and you're better off just judging your PO4 by your nuisance algae growth. Other than that, there's not anything else you'll need to test in an established reed tank. I do keep an API ammonia test kit on hand that hasn't been touched in years.
I've been wondering this also, I have red sea pro as of now and that mg test... ugh makes me pull hair. constantly all over the place... Anyone else have that issue?
Same, but if u just started pick up nitrate, nitrite, ammonia, ph. An api kit would be good enough for those but mg, calc, alk I would recommend salifert or red sea