need help asap!

Alright i think ive asked this before but i can't find the thread i did ask it so just asking again. My tank is 55 gallon with 20 pounds of live rock and 35 dry rock, live sand. hang on the back skimmer and canister filter and no sump. Nitrates keep becoming a problem, can i just return the canister filter and buy this instead http://ift.tt/Zaz3Oi



if i do buy this, can i run it all the time or just when needed? and should i buy the pump with it, cause i already have a powerhead/wavemaker for slow, if i added this, i would put it on the other side of the tank? Need some advice or details soon as possiable



Thanks