Results differ with test kits

[jabx1]

I have been using Red Sea Foundation Pro and Algae Control Pro test kits for over a year.

I used these same kits about 10 years ago and thought it was a big improvement over the API test kits I was originally using when first in the hobby.

Over the last ~4 months I have begun to question the accuracy however. I was consistently getting readings of 0 nitrate and phosphate even with increased feeding and no skimmer.

I was also getting very low Alk readings, usually below 7dKh. It was the winter and my windows have been closed for months so low Alk isnt surprising but below 7 readings after a ~20% water change (Reef Crystals salt) was strange. I have been dosing ESV Alkalinity (part 1 of ESV 2 part) and trying to get my Alk & pH up.

I finally decided to purchase some Hanna checkers and they came in last night.

I only did an Alk test last night with both the Hanna and Red sea tests.
Here are the results:
Red Sea: 7.89
Hanna : 8.7

Should I trust the Hanna which is brand new? Throw away the Red Sea tests?

 

[jabx1]

I have read mixed reviews about the Hanna Phosphate ULR checker.

Does anyone have experience using this? I would like to confirm that my phosphate is actually as low as the Red Sea test says it is.

 

[Sam22]

I have read mixed reviews about the Hanna Phosphate ULR checker.

Does anyone have experience using this? I would like to confirm that my phosphate is actually as low as the Red Sea test says it is.

I would trust the Hanna over the Red Sea any day my Red Sea phosphate pro was given me a reading of 0.08 for months and I’ve seen a thread on here with a few people saying the same. When I got my Hanna my phosphate was reading 0.4 I had my lfs test my phosphate and they also told me it was 0.4 so I chucked my Red Sea away and rely on my Hanna I use the Hanna phosphorus as it’s more accurate specially at lower ranges

 

[PatW]

I use Red Sea Pro, Hanna and Salifert for ALK.

HAnna: Advantages - digital read out. No interpretation of end point color. Gives results to nearest .1 DKH.
Disadvantages: results vary between reagent bottles.
Red Sea Pro - reads within .2 DKH.
Salifert - reads within .3 DKH.

Salifert reads the highest and by about 1 DKH.
Hanna reads a bit higher than Red Sea Pro.

The odd thing for me is they all seem to vary about the same amount from sample to sample. I was surprised that Hanna did not demonstrate to be clearly superior. If you went by the money, Salifert is the clear winner.