I have a small in-ground pool (20,000 gallon) I have considered incorporating into my ground loop using a heat exchanger so the pool water and loop water do not mix. Has this been discussed here before? I searched and did not find anything?

Household water use is minimal compared to geothermal use - so I don't see there being enough of it to get much heat from even when you consider that some of it is warm water and there is some biological warming. Using filtered septic tank water or gray water or even rain water off the roof for a soaker hose - that makes more sense to me.  Similar benefits + better soil conduction and no problems created if it fails.

Using a pool has been talked about alot here. search for posts by a user named brock