yikes! Listen to Steve-s!
right now your alkalinity is almost 17 dKh
. 11dKh is the upper end of acceptable.
If you plan to use additives like calcium and alkalinity, you MUST use high quality liquid test kits. dip strips can just be damaged too easily, and with the significant investment in live rock, corals, inverts and fish, you cannot afford to skimp on testing.
I'd say that's not enough circulation either. I have two MJ 1200's for my 40gallon breeder tank, which is a full foot shorter in length. This seems to be a perfect amount of circulation for me. I'd put another 1200 on there. Put them directly across from each other, and have them angle'd slightly up so they agitate the water's surface, and the current is semi-erratic.
I'd put the 900 in the back corner of the tank, angle'd up a little steeper for even more surface agitation, which will give better gas exchange. Lack of good gas exchange can cause CO2
buildup in the water, creating carbonic acid, which pushes your pH down a little.