Temperature Swings...to the cold side?

Greetings!

I've got a batch of 1.072 OG extra pale ale in the fermenter now. Yeast is US-05 dry. I'm using a swamp cooler and the occasional addition of ice to keep the fermenter cool. However I'm experiencing odd temperature swings towards the cold side whenever I add ice or more water. I have a thermocouple probe inside the fermenter. Without ice or after it has melted, I've been reading right about 68, but if I add ice in the morning and come back to check on it an hour later it's down to around 55. The lowest I've seen is about 52. Can a swing to the low temperatures and back up stress the yeast as much as swings above 77?

Never really thought of something getting colder when I added ice as odd....:cross:, but... It shouldn't stress the yeast as much as possibly cause it to go temporarily dormant. Any up/down swing isn't a great thing but given the choice, down would be the way I'd want to go. What is the ambient in your house? Have you tried not adding ice, instead adding some fresh cool water or just a couple cubes of ice? If you have your carboy or bucket wrapped as well as sitting in the water, you may not need anymore drop than that will already provide.