Hey Zorfox really appreciate your help on this and the informative links you sent.
When you say plantbrain lol do you mean Tom Barr?
Also are you referring to " If the tap has consistently high NO3, say 30ppm, then you do not add KNO3, instead, use K2SO4 etc."
So in my case if I do have high nitrates, I can just buy some K2SO4 work out how much I need to add to my 500ml solution, then carry on my EI and hopefully the plants will be getting there potassium.
If this is the case do I have to worry about any fish/shrimp coming to harm with K2SO4? I will do some research on it as-well.
I also forgot to ask you yesterday, I looked at the calibrating thread you linked, and for example my tank always shows 40-80ppm Nitrate its so red I cant tell which ppm it is but 80ppm sounds way to high for tap water, but if I calibrated it and tested a cup with 25ppm and the test kit shows red, its still going to be hard to determine my reading, as in theory if I tested a cup with 10ppm nitrate I could possible still get a red reading, I will certainly give it a try though and see what happens.
I don't know if you can recommend me any good test kits ? that are more accurate? I did some research on how accurate API nitrate kits are and a lot of people seemed happy to say they was accurate, and other's not so pleased.. are some api nitrates kits bad while another one would give me a better reading aka pot luck?
I still believe my Nitrate readings are not correct, so if I get a accurate reading then I can just dose the KNO3 for potassium, if not I'l have to find a place that sell's K2SO4.
MY water report says: Nitrate 50 mg NO3/I