Mine is currently at 16. I'll be measuring again before and after my next WC and then I plan to start dosing prodibio. If that doesn't do it, I'll probably look at vinegar.
+1 to water changes also less feeding. Do you have a fuge,if not this will help. How many fish do you have? maybe your overstocked. How much rock do you have? You may need more. Do you blow off the rock when you do water changes? You will be surprised how much detritus comes out you wanna suck that out with water changes.