USA College related CTR going down in July makes sense because college students are on their summer break. They're at the beach.
It's possible that whatever traffic you are receiving is not on the "buy" part of the buying cycle. Check your top keywords:
Are they product/service related?
Are they research related?
Are they unrelated to purchases?
Home improvement is probably taking a break for similar reasons. People are on vacation or buying vacation related products. Seasons bring on different buying patterns. Subscribe to email newsletter for various USA stores that feature a wide inventory of general products and stores that sell to specific niches. This will help you understand what buying cycles correspond to each season. Or you can try researching Google News using month/season keywords.