- Algae and mosquitoes.
Algae will thrive in stagnant water so do mosquitoes.
Algae will make your stock tank pool slippery and enjoying a good splash won't be possible anymore.
Mosquitoes may bring malaria.
to avoid these chlorinate your water. Or get a filter pump to clean your stock tank pool regularly.
Also, drain your stock tank from time to time.
If your tank ain't properly galvanized, strains of rust will start to emerge.
Other than that, using a lot of chlorine to clean your water will accelerate corrosion. Use chlorine sparingly to preserve your metal tank.