Some pools fail to respond to normal treatments, such as those outlined in our Green & Cloudy Water leaflet.  Even professional water testing and the accepted guidelines for treating green and cloudy pools cannot always determine the precise amount of treatment required, especially without a visual observation of the water.  Generally, when a pool fails to clear after being treated as recommended, the reason is one or more of the following:

  High levels of contamination in the water

  Phosphates or Nitrates in the water

  Densely established algae growth

  Poor filtration


High Levels of Contamination

High levels of contamination often happen without the pool owner realizing something is “different” with their water.  A build-up of contaminates (organic and nitrogen wastes) in the water create

A.  nutrients that feed algae and bacteria growth

B.   rapid consumption of chlorine

A water lab can test for combined chlorine.  This gives an indication of the presence of contamination, but the actual level of contamination is not easily ascertained.  High levels of contamination will cause rapid chlorine consumption.  Within a day or so, a normal chlorine shock can deplete chlorine levels to nearly zero if high levels of contaminants are present.  Thus, a steady, adequate chlorine level is difficult to maintain when large levels of contaminants are present.


Phosphates or Nitrates

Phosphates and nitrates are “super nutrients” for algae and bacteria.  When phosphates or nitrates are present in large amounts, killing the existing algae is much more difficult.  Likewise, with phosphates or nitrates present, keeping the pool water free of future algae growth becomes difficult.


Dense Algae Growth

As algae begins to grow in pool water, the water first turns hazy, then a green cast appears.  As the algae grows denser, the water will turn increasingly darker green and cloudy.  The most intensely dense algae growth results in very dark, almost black water that has visibility no more than a few inches into the water.


Poor Filtration

A key part of clearing any pool water is good filtration.  A filter that is not performing properly can be a reason the water fails to clear.  Filter systems should run 24 hours during the process to clear the water, unless specifically instructed otherwise.  After the “breakpoint” treatment (outlined below) there should be noticeable improvement each day in the clarity of the water.  If water clarity doesn’t improve each day, the filter should be inspected and serviced.  New sand, cartridges, or filter parts may be necessary.  MEMPHIS POOL has a complete selection of these parts and accessories.


What Is the Treatment? 

A strong “bomb treatment” is necessary to kill all the algae, fully oxidize contaminants, and filter out all the remaining particulate matter.   Understandably, the pool owner may feel they’ve already done this since unusually large amounts of chemicals may have already been applied.  Yet, large dosages of oxidizing chemicals are needed to hit the required “breakpoint and clearing” level for a pool.  No clearing can occur until there is enough oxidizing power in the water at a given moment to overpower the algae and fully oxidize the contaminants.


The Breakpoint Application Formula Is as Follows:

1.  Adjust pH to 7.0-7.2.  This is critical to assuring maximum effectiveness of chlorine.

2.  To kill existing algae and remove the nutrients that feed its growth, choose the appropriate application (a, b, or c) below:

a.  If you can see the bottom in the shallow end but not the deep end,  add 4# SUPER SHOCK ‘N SWIM and 3# WHITE LIGHTNIN’ per 10,000 gallons of water.

b.   If you cannot see the bottom in the shallow end, add 7# SUPER SHOCK ‘N SWIM and 5# WHITE LIGHTNIN’ per 10,000 gallons of water. 

c.  If you can see less than two feet into the water, add 10# SUPER SHOCK ‘N SWIM and 7# WHITE LIGHTNIN’ per 10,000 gallons of water. 

3.  If Phosphates are present above 125ppb, add a PHOSPHATE REMOVER.  If Nitrates are present, a portion of the water will need to be drained and replaced with fresh water.

4.  Add 4 oz. ULTRA CLARIFIER for each 10,000 gallons.  Run filter 24 hours.  Backwash/clean as pressure indicates.  Be prepared to service the filter if the water doesn’t clear in reasonable time.


Results to Expect

The water should lose its green cast within 24-48 hours. (If this does not occur, you must immediately treat the pool again using the formula above.) This lack of green cast indicates the algae has been killed and most wastes oxidized.   The remaining cloudy (milky looking) water contains filterable material that must be trapped by your filter.  As the pool filters, marked improvement in the pool’s water clarity should occur each day.  Likewise, a natural blue cast will appear as the water clears.  Many pools take 5-7 days to clear due to the large amount of material that must be filtered.  Be sure to backwash or clean the filter as the pressure increases.


Speed the Clearing

To speed the clearing after the application above, you can consider two options:

1.  Use SPARKLE FILTER AID on sand filters.   This product is added through the skimmer (about 2 cups) and coats the sand bed with a superfine filtration agent.  Fine particulate is filtered very fast; however, the pressure on the filter must be monitored and the filter backwashed frequently.  SPARKLE FILTER AID must be added again after each backwashing.

2.  Use FALL-OUT.  This is a product that flocculates all the particulate in the water and drops it to the bottom of the pool (overnight).  The dropped-out material must then be vacuumed manually the next morning with the filter in Waste position.  The user must follow the instructions on the bottle carefully to ensure success.  This is the fastest way to clear cloudy water.


Related Articles: 

Mustard Algae

Green & Cloudy Water 

Return To DYI Pool Care Main