Reasons why your Sand Filter might be the cause of Green or Cloudy Water: (Note: For all the details about these reasons, see below.)

            1.)  You have a Sand Filter (See Below)

            2.) You have Dirty Sand

            3.) You have Improper Sand Grading (Sand Grain Size)

            4.) You have old (Worn Smooth) Sand Resulting in Channeling

            5.) You have Broken or Damaged Laterals

            6.) You have not Back Washed Every Week for 2-3 Minutes.

Sand Filters:

            1.) Sand Filters, since they let particles smaller than 30-40 Microns pass right through and back into the pool, will require a longer running time by 25% more than properly maintained and functioning D.E. or Cartridge filters, in low hardness environments, to keep the water looking decent. 

            2.) Most “Pool Algae” is in the 5-20 Micron size Range. If you have a problem with algae, on a regular basis, get a filter that will filter this sized particle without “adding” filtration aids, that won’t plug up and cost you a bundle in replacement cartridges, and a ton of time cleaning. In other words, replace your filter with a Diatomaceous Earth (D.E.) Filter. DO NOT GET A CARTRIDGE SYSTEM OR YOUR PROBLEMS WILL GO FROM BAD TO COMPLETELY NON-FUNCTIONAL.

            3.) If you do get Cloudy or green or Cloudy Water with a sand filter, first make sure that the water is being pulled from the Bottom Drain, and Returned near the surface as close to the walls as is possible, creating a counterclockwise whirlpool, with the ripple on the water 3 feet from where the eyeball is located. (Northern Hemisphere) This will push all the dirty water down, and towards the center where it can be pulled out and filtered. Note: If the returns will force surface debris past the skimmer going counterclockwise, or will leave eddies where surface debris just spins around, you can consider going clockwise with no reservations.

            4.) Because of a sand filters poor filtration, green or cloudy water will require additives to the water or the filter to either clump the small particles into larger particle sizes or close down the spaces between the sand grains. The best additive, from a results and price perspective, is alum. After backwashing and returning the backwash valve to the standard operating position, toss ¼ cup of alum into the pool. When the pressure rises 5-7 lbs. Backwash for about 2 minutes, put back in proper operating position and toss in another ¼ cup. Repeat this process until the water is clear. Finally, after the water is clear, vacuum the entire pool, and immediately backwash one final time. Leave the equipment on 24 hours a day until the problem is completely resolved. Note 1: When you are first starting out with the alum, you “may” need to backwash every ½ hour. As the water gets clearer the time span between backwashes will increase. Note2: Make sure that all chemical readings are where they should be prior to starting this process, or you are just spinning your wheels.

            5.) Doing Sand changes because of consistent cloudy water are usually a waste of time unless the pool gets an extremely large amount of dirt and debris on a regular basis. This will cause dirt and debris to blow back into the pool even after backwashing for 2 minutes or longer, and will result in debris that is vacuumed immediately blowing back through the return lines. Another problem is broken laterals. These result in sand blowing back into the pool. I have had commercial size pools with residential filters that “Did not Need” a sand change and still kept the water clear after 15 years of usage. On the other hand I have had pools next to active farm land that needed one every year due to the winds blowing ½” of dirt into the pool every week. If you don’t have these problems, a sand change every 10 years might not be necessary. Look for the signs listed here, and make sure everything else is adjusted properly first. Getting cloudy water when you let the chemicals get out of whack is a guaranteed thing with a sand filter. It’s not the filters fault. Put in the additives and fix the problem and go on with life. If everything is adjusted as it should be, and the water turns cloudy, and the problem continues, consider a sand change.

            6.) That said, a sand change is about 1/3 – ½ of the cost of a new D.E. filter. If you are maintaining the pool yourself, and you stay on top of things and check it every week or two, a D.E. filter will keep your water from ever turning green again. (As long as the filter is properly maintained, backwashed and cleaned according to the manufacturers specs, and the water flow is adjusted as it should be, even if you put in no chemicals the water will remain clear. Yes your walls will be green and black slime, but your water will be clear. If your attention to detail is so poor on water chemistry however, chances are you will destroy the grids in a D.E. filter. Stick with the sand. If you have a professional who knows what he is doing servicing your pool, or you service your pool and stay on top of things, you can cut your operation costs by about 25% both in electric and in chemicals because of the added filtration. Usually this means that those that are “attentive” will get their additional costs back within 2 years, and the water will truly sparkle due to the upgrade. 

            7.) Again, if you “MIGHT” be a little careless, or you “MIGHT” turn the property into a rental, STICK WITH THE SAND FILTER even if the renters let the pool turn into a swamp, drain, chlorine rinse the pool, dump an extra gallon of bleach into the filter and let it sit for an hour, backwash for 5-10 minutes, and you should be back in business. Every time you make that mistake with a D.E. or a Cartridge filter it will cost you $200-300.00 and a cartridge filter can never clean up a bad case of algae in the water, without a tremendous amount of time and effort.

            8.) Upkeep on Sand filters usually ends up being about 300-500 every 5 years. (Note: Never get sand filters that are held together with dozens of bolts. It is almost always more expensive to do a sand change on this type than it is to buy a whole new filter.