ATI ICP-OES testing compared to my own testing

[Frogger]

I just received my first analysis from ATI for my tank water and I did a complete test of my parameters using normal available test kits at the same moment I took the sample and sent it in.

What i have found is I am only really close in 2 parameters salinity and copper. Everything else is off and some by quite a bit.

Alkalinity I tested 8.4 with hanna and 8.5 with Salifert. The actual number was 8.1.

Calcium- I tested 430 with Salifert, 450 with Salifert Strontium test kit. The actual value was 409.

Phosphate ppm tested using hanna ULR at .043 actual was .01.

Nitrates using Red Sea Pro at 1.2ppm it was .01ppm

Mg tested using salifert ppm at 1500 actual is 1415ppm

K tested at 370ppm Salifert actual is 452.

Strontium tested at <3ppm with Salifert actual is 7.8ppm.

So based on my testing I was running GFO to lower phosphates and worried about my Magnesium being too high and my Strontium being too low. In the end ATI is recommending that I stop GFO add phosphate, iodine, molybedenum, Vandium, manganese and Floride everything else looks good. I also need to change my DI resin. Silicates are a little high

How do I trust my personal readings and make appropriate changes when the numbers are not even close? I have no reason to doubt ATI's numbers

And by the way copper was only close because both tested none. I believe the Salifert cu test kit is only really designed when treating parasites in a quarantine system. So that was a no brainer.

I chose ATI because from what I read and saw they appeared to be the best and they also test RO water as well.