new2saltwater

i did full test at about 11 this morning. i read that time of day can effect ph though so i tested ph again about an hour ago and still reading 7.8, which is a little strange because it has always been steady at 8.2.

Hi, im new to the saltwater hobby and have had a 100 gallon tank for about 5 months. everything is doing well in the tank but i have never been able to measure the calcium with my API test kit. it reads higher than 520ppm when tested. all other parameters seem good. using reef crystals salt. PH was stable at 8.2 but when tested today it is at 7.8. alkalinity is at 7dKH. I bought a magnesium test kit yesterday and it is at 1200ppm with my ELOS kit. Could my API test kit for calcium be inaccurate?