Low Cyanuric Acid or (Stabalizer). PH & Alkalinity too high. High amounts of oxidizeable materials in water,organic debris,plant,grass,soil,heavy bather load,urine,bacteria,etc....
Chlorine is effected by sun, air, temp and bather load. You should check first to see that your stabalizer (cyanuric acid) level is ok, 30-50 ppm. That will help chlorine stay in water.
Pile a small line of crushed shells along the pool deck edge. The sensitive worm's tummies will prevent them from crossing over to the pool. The problem is the worms crawl out during rain, then when...
Try finding a fake swan or large bird u can keep floating in the pool. Other wise make sure you "shock" the pool weekly and also add Natural chemictrys "pool perfect plus phos free on a weeky basis....