Ca tends to precipitate at higher temps**, this might explain why Ca dropped w/ the more info of your higher temps for a day. dont chase pH, it will fall in line when "the three" are in check, your salinity is right, aeration is in place, and the temp is stable***. all those "recommended" readings in the chart above are at 78. as temp rises, Ca precipitate kicks in at "lower" levels. ie. 520 @ 78, vs 460 @ 80 (examples, i dont know the exact numbers, and it will vary based on many factors in each system)
I think somewhere in the middle of Ty's thread we all had a discussion of which type of salt we use. it seems most use the cheaper "reef" mixes, since we dose or use reactors more than we water change. why pay extra for salt, when you have other systerms maintaining those values? the bottom of my "salt" barrel is lined w/ precipitate & other things settling out, since my garage is friggin warm/hot. but using this water in a water change doesnt impact my numbers, aside from dropping nitrate and phosphate (i have a pump and airstone in there).
** http://reefkeeping.com/issues/2005-07/rhf/index.php#15
*** http://reefkeeping.com/issues/2005-07/rhf/index.php#13