I have a 20,000 gallon pool and it has mosquitoes in it. We just replaced the Filter system. I wanted to see if I needed to drain the whole pool or if I could just treat the water to start using the pool for swimming. Please let me know what you recommend.
You should be able to treat the pool and start swimming as long as the water is being circulated and treated properly. Also, often times even in significant problems, a complete drain and refill is not necessary. A partial, 1/3 or 1/2 is sufficient to bring good fresh water in to freshen up the old "dull" water.