Pool drainage/leak

[pooldesert]

We purchased a home in September with a pool. We are new to caring for a pool. In our last rental a pool guy took care of everything. We had a pool guy come by to help us get the chemicals balanced and learn what to do. We were told that our filter was too small for our pool. A replacement filter was recommended for $800-$1000. We are not ready to do that yet, so the guy cleaned the filter. The vacuum and the water feature worked very well after it was cleaned, but we had a new problem. The pool equipment sits on cement. After the filter cleaning the sand/rocks/dirt near the pump was messed up. Instead of the dirt/rocks/sand going all the way to the cement, there was a collapse of the earth in the area and it left a gaping hole under the cement slab. It was off-color for a long time. I thought it would dry out and we could put it back, but it has not dried out. I am wondering if I have a leak somewhere. The ground there is always wet now. It was not like that before. We had a guy come out as part of our home owners warranty, but he said there was nothing he could do because it was underground. I was going to do the bucket test, but we have been having lots of inclement weather. We normally have sunny days. This area was not wet due to rain. I tested other areas by putting water on the dirt and seeing how long it took to dry up. It was within a day. I was thinking that perhaps it was the skimmer since the hole where the skimmer is has about the 2 top inches without plastic. It is just cement and there are a few gaps that water could leak. I was also wondering if it could be the water overflow since we did see some wet spots on the cement under that valve. Help. If I call someone for help, who would I call anyway? I already wasted money on a second pool guy who pretty much did nothing. I didn't want to call the first guy back after the mess he left.