So background- moved into a house that had sod put down. Don't know how they cared for it, but when I moved in the grass was over a foot tall. The grass was very green however way too tall. After much pain and time I got the grass down to a normal length when I noticed that despite the top of the grass being green the lower half was all yellow/brown. Another thing that was noticed that many areas of the ground was wet - even though I had not watered the lawn in a week. - Weather- hot in the day, cool at night.

After fertilizing and watering normally I noticed that despite some yellow areas turning green there were areas that did not improve. After further investigation I noticed that these areas still were very wet with no logical reason while other areas were dry. Started to dig around and the wet areas actually had what seemed to me "rotten" grass, very wet and mushy. Now I looked online everywhere to find out what is going on but couldn't find any info. To me it seems that if possible the sod is rotten? These wet areas have grass that is very dark grey/black. I have never dealt with this and am worried that I have to pull up all this "rotten" sod. But wanted to get people's opinions before I go on a witch hunt against the rotten sod. Thanks ahead!