However, unlike the milk in your coffee it does not get "used up". If there are areas of poor circulation it is very possible for there to be localized areas where the chloirne is "used up" which can allow algae to grow. Running higher FC is not really going to solve circulation problems. More frequent brushing can help. These are essentially 'stagnant" areas where chemicals like chlorine can become depleted and no new reserse is carried in fast enough to prevent problems.