Rather than fighting with the nitrates with chemicals as this only masks the problem , you first need to find the cause most likely overfeeding from past experience . 50% water change + 50% water change will remove the excess nitrates . if you keep up with maintenance your 10% water changes will keep you in check ,
the biggest thing a lot of people over look is cleaning out media boxes filter socks sump ect . I do this bi weekly if you saw the crud I find in mine just imagine whats hiding inside yours . periodically I clean the skimmer as a lot of times you will find dead snails in it .
proper maintenance done during water changes can solve your issue a long with understanding whats going on , I suggest starting a log start by testing every other day along with listing everything you did to the tank daily 2/3 weeks down the line you will see whats happening as things change ,
I use mine like a bible I pinpoint whats wrong faster as I can go back and say . ok this started on such and such a day what did I do different , look I added this to the tank or you remove something that's when things went crazy,
all this information your writing down is a gold mine now you can stop bad things before they happen ,
I ask myself would my tanks be as nice if I didn't keep a log ? my answer no
why the log helps you better understand the chemistry of your tank .
you can ask me what did I do to my tank on march 3rd 2011 .
nitrite 0 ppm
nitrate 5.0 ppm
that was high for me
ammonia .25 ppm
ph 8.2 ppm
phos 2.0 ppm
just looking at the nitrate and phosphate I see something happening
calcium 480 ppm
clean inside glass
blow off rocks
remove old media and replace
clean external filters remove all crud
20% water change to curb the nitrate and phos building
added a hammer and a zoa
it's awesome to be able to look back to see what was going on you can compare notes from the same day a year ago see what has changed