I have caught trout 8 feet down in 35 feet of water, on bright sunny days. Keep changing the depth of your tipups until you find them.
When I get my tipups ready, I make a bunch of Fluorocarbon leaders that are 2 to 3 feet long. I also use # 18 or # 20 hooks on these rigs. Fluorocarbon fishing line is nearly invisible, and the small hooks have increased my success rate.
The small hooks also help to keep your minnow more lively.
Hope this helps,
Wiener