How do i keep nitrates under control in my tank (180g)

[Quo Vadis]

OP, you could try running a denitrification reactor. They're easy to build or buy. Just pick a suitable carbon source for the anoxic bacteria and try not to overdose. Alcohols, vinegars, and sugars are good potential carbon sources, or you can buy a commercially available product. We run a large version of these reactors at work and they function very well. The water coming out of the reactor usually has about 10% of the nitrates as the water going in.

Do you have a link to more info on this? Haven't heard much about this idea before?

 

[Pomatomus]

here's an overview of the process http://en.wikipedia.org/wiki/Denitrification

but if you want to get an idea of how it's used in aquariums, look of vodka dosing. It's popular in reef tanks because 1ppm of nitrate causes reefkeepers to have heart attacks

Here are examples of commercially-available media reactors and carbon sources:https://www.google.com/shopping/product/15272307836579485556?sclient=psy-ab&q=media+reactor&oq=media+reactor&pbx=1&bav=on.2,or.r_qf.&bvm=bv.73231344,d.aWw,pv.xjs.s.en_US.REnTyI5MwPc.O&biw=1536&bih=762&tch=1&ech=1&psi=DDz0U4PiBo2SyASMroCQDg.1408515097917.5&sa=X&ei=Nzz0U_CFCY6LyASR3oDoAw&ved=0CJ8BEPMCMAM

and http://www.marineandreef.com/Two_Little_Fishies_NPX_Bioplastics_400ml_p/RTL42241.htm?gclid=CJes8dqXocACFahj7AodzCkA1w