I have a big water leak in the middle under the fan and engine belts, what could cause this? Water pump, a hose? How to fix this? K-leak sealant or water pump replacement, I don't know, thanks.

Sounds like a water pump. If your water pump is working, both your upper and lower radiator hoses will be hot - if not, water pump replacement time. Do not get whatever is cheap. Do a little research and good ones cost about the same as junk ones that will not last. Your biggest expense is the labor, not the pump. So go for quality.