Agree with above, keep up with water changes daily for now. Before your WC make sure you are stirring up detritus from the live rock to be siphoned out. Also make sure you sihpon out any detritus that has settled in the rear chambers. You may also want to take a look at siphoning junk out of the sandbed, but split this up over a few days. I'd only do about 1/16 of the bed at one time so you don't stir up too much..
Also replace your filter media and carbon with brand new ones from the LFS.
Has anything changed with your water supply? Maybe you need to replace RO/DI filters (or your LFS does). You can test new water to see where it's at. Lastly, if you are mixing your own water, have you received any notice about a change to chloramines being used to treat your water supply? This has been happening a lot in my area and could explain spikes like that if not accounted for.