Yellow algae in a pool can be a hassle to get rid of. Simple chlorination or superchlorination won't do the trick. You have to include algaecides as part of the treatment. While a variety of algaecides will work against yellow algae, you have to pick the right one depending on which stage of yellow algae treatment you are in.
As effective as algaecides are against yellow algae, they are more effective with the proper pool treatment prior to application. Scrub all pool surfaces to help break down yellow algae cell walls. Then scrub the surfaces of objects recently exposed to yellow algae. Finally, superchlorinate or "shock" your pool 24 hours prior to algaecide application. This can further weaken yellow algae before the algaecide kicks in.
Quat algaecides are among the lower-priced algaecides. Short for "quaternary," quat ammonium salts act as surfactants that break algae's cell walls by lowering the water surface tension. Thus, you can kill yellow algae's cell walls by "wetting" them. Quats are most effective with green algae but can also be used to kill yellow algae if applied at the right instance. Use quats if you have had previous episodes of mustard algae in your pool and you suspect that it's coming back.
Polyquats are a more concentrated version of quats. While quats are usually concentrated at 10 percent, polyquats are effective in 60 percent doses. They are also more expensive but have little side effects and can kill visible yellow algae strains. Use polyquats if you've recently killed yellow algae and want to prevent a return, or if your yellow algae are just starting to bloom.
Copper is also effective against yellow algae, but use it with caution. Copper algaecides are typically applied weekly in small concentrations to prevent algae growth. One advantage of using copper algaecides is that you can swim in your pool almost immediately after application. However, if used improperly, they can stain your pool walls or cause heavy foaming. You also shouldn't use them to kill yellow algae if you have a biguanide-based sanitizing system in your pool.
Silver is another metal used in algaecides that is proven to be effective against yellow algae. Colloidal silver algaecides attach to your pool's walls and surfaces, making them stronger and more resistant to yellow algae. It's also effective against bacteria, which can strengthen your pool's chlorine effectiveness by reducing the amount needed. Be careful not to use high concentrations in direct sunlight, or you'll turn your pool walls black.
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