I need help figuring out what to do about ammonia smell in my coop

For 15 years keeping chickens I've used sand or coffee grounds and scooped poo daily, but thought I'd try deep litter this winter. In November I cleaned out all grounds, put dn 4-5 inches medium pine flake, sprinkled zeolite & add thin layer every 3 days or so. I turned the bedding today and its WET underneath and ammonia is bad.
We have 20 standard hens & 4 bantams. Coop (converted amish built shed) is 10 x 11, windows are at roost height so I only open them in morning, 3 small vents at 10 ft high. If its this bad in 6 weeks I cant go all winter- I don't understand what I did wrong?