I was away on a work trip and just got back today. I went out back to test my hot tub water only to find the cover flipped half open, my @ease on its side (but not flipped) and the water down about 6" from the fill line! I never used the cover snaps since it's in a locked and small area surrounded on two sides by a 6' fence. I never even gave any thought to the high winds due to the nor'easter a few days ago.
I immediately grabbed the hose to start filling it back up and then tested my water. Chlorine levels are ok, pH is very low, total alkalinity is very low, and calcium hardness is high. I just added some alkalinity increaser and will retest in an hour to see where I'm at. Previously to my work trip I tested the water and everything was perfect.
Lesson learned... use the cover snaps!!!