Can overheating be a problem ??


Reefing newb
i just wanting some advice. Had 250lt mixing Red Sea coral pro for water change I checked salinity as always 1.026. Didn't (never do ) check other mag alk cal.
Unknown To me thermometer in barrel was faulty and water heated up to 32 degrees. Replaced therm and waited for water to cool to. 26 did water change and now testing the tank.
All parameters are low. Mag 1200 norm 1350. Alk 7.7 norm 8.6. Cal. 390 norm 450 ? I had run test. 3 days prior to change and all normal.
My question is can the overheating cause a loss of these elements ??
There was also a lot of sludge in bottom of barrel ( never normally. Could this have caused the oil slick on top of my tank last week ?
I am now in process of mixing up another 250 today as that's seems a better option than dosing the large amount I would need to get everything level again ? Thought please. ?
Do you always check the big 3 in a new barrel of asw before change. ??