Crystalline structures on aquarium lid

[FeldmansFish]

I was doing a water change when I noticed these salt like structures around the top of my aquarium. What is it? Could it be because I have hard water?

 

[Aquatic_Adam]

Yep. You have hard water. When the water evaporates, it leaves some of the salts behind. That creates the white residue. Nothing more than some elbow grease to take care of it really!

 

[Rivercats]

You can also put a little white vinegar on a rag before rubbing it off as the vinegar will help cut through the deposits. And it won't hurt the tank or in habitants if you would accidently get a touch in the water.