Stinky Water - My Pool Smells Like Poop

[waterbear]

Sounds like hydrogen sulfide. Are you filling directly from a well?

My thoughts exactly! It can also be coming from the sand filter. bacteria can grow under the right conditions (anerobic) in the sand that produce hydrogen sulfide gas. It's actually a pretty common problem with aquarium sand filters under anerobic conditions and can kill of an entire tank or pond when it happens. If you open the filter and the sand looks black in some areas (and has a strong sewer smell) then you have found the cause. IF it is hydrogen sulfide than chlorine is the answer but with a CYA of 80 ppm you are going to have to bring it up to a minimum of 20 ppm FC and possibly higher. I would also stick a garden hose in the open filter, turn it on and let the water overflow while CAREFULLY stirring the sand and breaking up any clumps with a broomstick or something similar. Be very careful NOT to damage the laterals on the bottom of the fllter. Once the overflowing water is clean you might want to dump a gallon of bleach directly into the filter sterilize the sand.