Did a bit more hunting round today while I was at work. Emailed tech support at red sea.
It must have sounded like I was questioning the accuracy of the kit lol
Here is the response
Thank you for contacting Red Sea.
The accuracy variation quoted of 0.05 meq/l is as you correctly suggest 0.14 dKH, this error factor is added if the dKH is 1.0 or 10 as you suggest, the test kit is designed for use on Sea water aquariums with an optimum dKH range between 8 and 13, the test kit will give you a suitability accurate result in the optimum range.
Whilst the test is easy to perform there are very many factors behind the test that can cause the test to vary, the pH of your aquarium being one of them, this variation would add to the error at a very low range but as stated in the normal range we are confident the test kit works with a high accuracy.
Regards
Kevin Davies
Technical Support Manager
Red Sea Group
So it would seem that there is a range in which the test is more accurate as they are not expecting to typically see a dkh of less than the lower value of their "optimum range"
Hope this helps?
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