I dont want to be proven right by any means, it just seemed an awful lot of KNO3.
It depends on how much you have dosed up to now as to what you should do next, fish will survive up to 100ppm no3 after that you are into the unknown, basically its poisionious for them at very high levels, some fish will be more susceptable to higher levels of no3 than others.
But i doubt you have dosed anywhere near that amount if you have been doing the weekly water change, if the fish look ok i wouldnt worry to much about it, although you will know best as to how much you have dosed since the last water change, even a partial water change would help if you think you have very high levels, and a major 50% plus water change if you think you have dosed serious amounts of KNO3, but you know best on this one.
Each tank is different as to the uptake rate, but i suppose a typical tank might use anywhere between 10ppm and 30ppm per week, like i said in total i use 20ppm per week KNO3, in the beginning you really have to test, with a good testkit......but any testkit can be off and this is why its good you asked rather than kept dosing the KNO3.
Just check you did the test correctly with the testkit, some nitrate testkits you really have to shake the bottle before you will test correctly with the B solution or the second bottle, might be worth a try rather than buying another one.......make sure you shake the bottle for at least 30 seconds and then do the test.
To answer the question.......i would normally dose 10ppm at water change and this would bring me to around 15ppm, and then i would dose 5ppm twice the following week, your normal routine could look something like that as well.
The more i think just double check you shook the bottle for at least 30 seconds before you tested.