No, that was a good catch, thank you! I confused myself looking at the spec sheets on Hanna’s website! I re-worded my above post, but while the margin of error for each checker is actually close and either should get the job done, the 736 becomes more accurate at that ultra low range because it’s measured in ppb, so while at a higher ppb the readings may not vary much between the 736 and 774, at the lower range closer to 0 ppm, that more precise reading will be more helpful for those looking to strictly keep phosphates below .03. The 774 margin of error of .02 would be too much to trust.
For example:
HI-774 reads at .03 ppm, it could be .03 ppm, but also could be .01 ppm or even as high as .05 ppm.
HI-736 reads at 10 ppb (or .031 ppm), it could be accurate but it could also be 5 ppb (.015 ppm) or even 15 ppb (.046 ppm). This example is why I was saying the margin of error is similar. The 736 margin of error, in this example, is not far off from the 774, but it matters more the closer you want your phosphates to zero. And I’m a nerd lol.
With all that being said, either will do just fine for most people, with the 736 maybe more suitable to those keeping an ULNS.
Here’s the conversion chart for PPB to PPM if anybody wants to peek at it: