What do test kits measure in?

[BlackShark11k]

I just purchased a new NitrAte/n03 test kit today since i ran out of the regent in my all-encompasing test kit... my question, this new kit measures nitrate in milligrams per litre (mg/l)... do other kits measure it differently, I seem to recall having a test kit that read nitrAte in parts per million or something like that.. I recall reading an article in either FAMA or AFI that said test kits measure in 2 different methods, and you can convert them by dividing the larger one by 4 or something..

If anyone got any sense out of what I just said, let me know if you know anything. I have a feeling this thread is a long shot.

I'm a little frustrated and confused today because I took a nitrAte test of the water in my new grow-out 55g, and i got about 35 mg/l of nitrate... and the tank has all brand-new water with no fish

EDIT MORE INFO: It might be because I have two different kinds (?) of tap water or something IDK. But our water comes mainly from a well and i normally have used well water, but its insanely hard too.. i think pH or 8 as well. I get well water out of the hose and the coldest water in the kitchen (if you turn the thing to the coldest possible). We also have soft water which comes from all the faucets, and i don't know anything about the parameters of it, but I do know that is has water softener salt in it... hmm.

So yeah, im confusing myself and probably whoever is reading this..

 

[12 Volt Man]

mg/L is equivelent to one part per million (ppm)

so you don't have to worry if the two kits give different units, they are the same.

its been a long time since I did the math showing why they are equivelent, but I recall it uses the density of water (which is 1 gram per cubic centimeter).