White filmy stuff in top of Pro Mix

[Jsick098]

This is the 3rd grow in my tent and 3rd grow using pro mix and ive never encountered this problem.
Humidity never goes above 60% tempt is on the hotter side 80-90 degrees

 

[TurboBucket]

Hard to tell from the pic. Looks like it's just hardwater deposits. Scoop a little bit out, if it's hard and crusty it's some sort of mineral buildup. If it's soft and spongy it might be bacterial or maybe a type of mold.