1) what kind of test kit do you use?
2) If you say API go get a hanna checker or Red Sea test kit (just my two favorite) people also love Salifert.
3) What kind of salt do you use?
With all this being said there is a chance this reading of 3 dkh. However, theres a better chance your test is wrong or there was some variable ruining the results. Try testing again with a different test kit, if possible, or the same one. I stay away from chemical warfare, dont use buffers unless life is at stake!