The tank is only 14 gallons so it would be really easy just to change 100% of the water. This is a common approach for small nano aquariums and can be used as a long term maintenance plan or a temporary solution for nitrates and other contaminants.
Some links you may find useful
http://www.advancedaquarist.com/2010/4/aquarium
http://www.reefkeeping.com/issues/2005-10/rhf/
Also I'll note your temperature is quite low for an SPS tank. In addition with lower temperatures you'll likely see more fluctuations due to external temperatures.