Seems like what you say.
But when I used to use api,I found best to read test with test tube infront of white on card in natural daylight and the light behind me ( so stand next to a window with your back to window.)
Light from sun and light from bulbs different and can slightly change the colour we see .
Alot I read say a nitrate of 5-20 is what they aim for,but seen alot of nice tanks with much higher nitrate than yours,mine runs at 40 ppm but with cheaper zoas/softies/lps and few sps and everything seems OK and no real issues with algae or anything so your 30ppm should be ok with a fowlr,but just keep testing and see if it rises or falls or stays same and adjust your water changes and any other means to reduce your nitrates accordingly is what I would be doing if me.
Alot will say api notorious for false readings so you may or may not have 30ppm anyways.
I know if I test with api or salifert,I get nearly identical readings but I'm not so stringent on wanting exact numbers and no high end corals in tank,maybe my opinion change as I go more Into this hobby as only 14 months in so still a newbie ^_^
But whilst you still using the api,just follow instructions exactly as says,use stop watch when shaking,rinse out test tubes after use and all that.
Good luck