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I own a residential/commercial pool   construction business in Ohio.

We have had issues on three different residential systems, where the

pool filter sand is "clumping" inside the pool filter. All three are the same:

less than 30 days into operation, hi-rate sand filters using Triton filters,

salt systems using Pentair salt generators. The filter sand has becomes so

hard and "clumped", we have had to use hammer and chisel's to remove?

Any thoughts? We've opened over 30 pools this year, and, to the best of my

knowledge, it has only happened on three. What would cause the sand to

harden, clump, so quickly?

Thanks for any input



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I have heard that if you add salt or calcium less than 30 days after doing a plaster job, You run the risk of the salt pulling the unhardened calcium out of the fresh plaster. Excess calcium + plaster sediment + sand = concrete. I was not sure if this was true but it sound like if the circumstance is just right it will.

I don't believe that salt will cause this however calcium, plaster dust or slurry from the new plaster can. I would look at hardness and TDS. Typically, your pH and /or alkalinity would be a good stretch off to have this happen by means of TDS or calcium hardness. If that wasn't the case, I'd go back to plaster dust or slurry. This stuff gets washed into the main drains or is filtered out in the initial start-up and attaches to the sand. (assuming that it is an aggregate finish)


Definitely sounds like calcification of the sand bed, from whatever source. I've had to destroy filters before to remove the media and install new filters.

Another reason over time this happens is poor flow rates. Driving the water too fast andprofanity filter removed this word the filter cycle can create channels in the media bed which means only some of the sand is actually filtering debris and it will also go too deep into the bed. Too low of a backwash rate will not clean the media properly. Too high a backwash flow rate and you can literally sand blast the filter body and destroy it. Too much can also cause such a sandstorm inside the filter that the debris you are trying to clean out will actually get swirled into the bottom of the filter and can plug up the laterals. This itself can eventually lead to channeling and increased head loss which of course leads to lower circulation and filtration rates.

Dear Mr. Larson ,

Thank you for your reply and time .I would like to ask you what is the proper level of Ca harness in inside tiled pool ?

The above pool 's Ca harness was between 170 to 240 ppm .

I look forward to hearing from you ,

Best Regards ,


That makes so much sense.

I am with the others who responded: this sounds like calcification due to bad water chemistry, usually associated with new plaster.  Although it is possible to get calciifcation of the sand  if there is high calcium level in the pool already and/or in the fill water.  Ignoring the pH and other saturation index factors is never good - add these factors to the chemistry of new plaster and you can make concrete right inside your sand filter!    Since you service the pool you probably are following correct chemical procedures, but the last time I saw this happen my customer was, without telling me, shocking the pool  with calcium hypochlorite.   I only found out because a windy day blew his empty 5lb. cal-hypo container into the pool and it was floating around when I got there to chisel the concrete-like sand out of the filter. 

Dear Bryant ,

The same scenario occurred to me last month .But , over there ,the sand filter was galvanized one and hammer and chisel did not work ;therefore, we diluted Some hypochloric acid (33 %) and poured on the filter media ,and after an hour it softened some portion of the sand filter and we continued this way until we removed sand from the filter .I took some photos of it and you shall find them here.

With regard to your question , Carbonate Calcium and other mineral components which dissolved in water can cause hardening sand .So, back washing and balancing the water of pool are paramount for having a pool with out chemical or physical problems .

Be careful, safety comes first ,

Best Wishes ,


This is a YouTube video showing sand that turned to stone, turned back to clean sand:





Dirty filters are like a dead rat, they drag the pool down and are the leading cause of unhealthy pool water. Filters do what they are designed to do, trap contaminants. The problem is that sand filters can't backwash themselves clean. Plus, all sand filters channel when dirty.  They also have the highest levels of bacteria in the pool, may be full of parasites (about 8%), biofilm, contaminants and oils. Simply backwashing a filter will not remove these contaminants. 



Importance of using a quality sand filter cleaner on a regular basis:

#1 reason, a clean filter will lead to better pool water. 

-Clean your sand, don’t replace it

-Cleaner, clearer water with reduced combined chlorine and eliminate channeling

-Remove oils, biofilm, scale and other contaminants for safer pool water

-Better air quality and a safer environment for swimmers, teachers and maintenance personnel

-Swim teams will experience improved performance, and will be able to train harder with reduced disinfection byproducts, reduced Trihalomethane (chloroform) and reduced combined chlorine

Guys, we are looking for samples of sand that turned to stone for further testing of our sand filter cleaner.  In consideration of your taking time to send a sample, I will send a free gallon of our sand filter cleaner.


We are also looking for unusual debris in filters to test our sand filter cleaner.




Bill Soukup

Technical Pool Solutions




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