HEHE I love this thread...
When I started reefing I started with API test kits... and all I can also vouch for their low quality test kits... you get what you pay for...
From API i went to ELOS which was a good step-up although still not satisfied I bought Red Sea test packages like the foundation (Ca, KH, MG) and this seemed to be good then I purchased the Red Sea Color test kit (K,I, Fe) and they seemed to be OK until the Red Sea test kit started to crap out and I wasn't getting a proper reading due to color discrepancy... The Red Sea KH solution will get tainted if you recycle whats left in the syringe...
Then i bought the Hanna Alk Chlorimeter along with Hanna Ultra Low Range Phosphorous Chlorimeter and holly molly what a breakthrough...
I test my alk every 3-4 days and sometimes every day and adjust my dosers accordingly as it literally takes 1 min to do a test and there is no color guessing here... just the plain number...
Now I wish they had the checkers for Potassium as well...
And to wrap it all up, each person is different and will use different methods to achieve the same or close end results and that's the beauty of this hobby... just because one method works for one person, doesn't mean it will work for everyone else and its mainly due to many factors like time, cost, ease of use and many other factors.
For example I use all brands of test kits according to whichever I think gets me the best results and also the ease of use is critical as I'm not the best when it comes to colors...
Examples:
For Amonia/Nitrite i use API
For Nitrate I use ELOS
For Calcium/Mg I use Red Sea and test against API if bored
For Potassium/I/Fe I use Red Sea
For Alk/Phosphate I use Hanna and I there is no way I'm going back to any other test kit (wish all test kits were Hanna)
Now is that what I use and that's what works for me, but doesnt mean it will work for everyone...
Now API is the wort test kit possible
if you want proof go to the pharmacy and purchase a 5ml or 10ml syringe(very inexpensive 50cents at most) and add 5ml to the vial... you will be amazed to see their 5ml line is not very accurate and I think its off by .5 to 1ml out of the total 5ml of tank water... That, right off the bat can be a discrepancy of 10-20% of the end result if not more