Rheem heat pump issue

This year our heat pump seems to only be heating the water about 2 degrees in an 8 hour run cycle, it usually does better than this. The filter is clean, the coils are clean and good water flow. The air coming out of the top is about 8-10 degrees cooler than the outside temperature but only in one side of the top. The other side is only about 3 degrees cooler. We have a 15000 gallon inground pool with a rheem heat pump and outside temperature is around 80.
I would appreciate any suggestions that anyone can give.
Thanks