You can safely do a 100% WC

All the denitrifying bacteria is on rocks and sand. You won't get any where doing small wc as the dilution rate is small

Start feeding less add some mechanical filtration to sump. Ie filter floss or sock. Look into carbon dosing of some sort. Vsv,prodibio etc

Some good info for you

http://www.reefkeeping.com/issues/2005-10/rhf/

Really good info so my best bet is do a 100% water change right?
I kinda afraid to do that but seems safe according to the article
Cus i dont want take my chances and loose everything in my tank :'(