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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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Any filter improperly sized and misused will lead to problems. Sand filters CAN and DO backwash themselves clean IF the flow is correct. I have personally seen many sand filters 10 plus years that were still fine. And of course it seems even more that weren't due to either excessive flow or lack thereof.

I will still maintain that from a visual clarity standpoint sand filters perform pretty much as well as DE or Cartridge, all things considered. I have seen poor water on DE and cartridge and awesome on sand. There are many factors to safe, clean water that don't take a fortune in chemicals or wasted dilutions  and unfortunately a lot of things seem to get overlooked too often.

I do agree that sand filters are when used properly and agree that cartridge and de can have issues.But I dont know of a sand filter that back washes its self ? who's  filter ? is it res. or commerical and what people/ homeowners seam not to know is "what the rinse is for"


This thread is about two different problems with filter sand:  1) calcification of sand causing the sand bed to become one piece of hard rock - which is caused by water chemistry problems and 2) dirty sand that has greasey lumps of sand (mudballs) which is caused by bather body oils, suntan oils or organic sprofanity filter removed this wordfrom trees, and sometimes pollution from vandals or even un-burned airplane fuel. 

Calcified sand might be corrected by an acid treatment, but I have never had any success with that.  Dirty sand can be treated with chemical de-greasers, and maybe enzymes.  Enzymes work better as a  preventative measure because once the sand starts getting formed into mud balls the enzymes do not penetrate into the ball .

I agree with Rick Larson that sand filters can be just as effective as DE or cartridge filters, but the key ingredient is  filter flow rate.  Cartridge and sand filters water quality suffer greatly from too high a flow rate.  Note that by "too high a flow rate"  I don't mean just exceeding the manufacturer's maximum flow rate.  High rate sand filters have a stated max of 20gpm/sq.ft. , but that rate produces marginal water quality- the really small particulate is pushed through the sand bed.  Keeping  a high rate sand filter in the range of 12 to 15gpm/sq>ft. will result in water clarity close to, or equal to,  a DE filter. 

When you read a chart from a cartridge filter manufacturer did you ever wonder why there is a big difference between "residential" and "public" filter rates?  Do the bathers have different size dirt on them?  No, the manufactures use NSF guidelines for "public" but put anything they like for "residential".  Stick to .375gpm/sq.ft. for cartridge filters as a maximum.  I prefer .333 gpm/sq.ft. for best water quality. 

The flip-side of the filter performance is proper backwash flow rate. High rate sand filters need 20 gpm/sq.ft. to backwash well.  Usually, there is much less pipe on the waste line than the return line, so backwash rate is usually greater than filter rate.  But don't make an assumption. Do the head calculation or install a flowmeter on the waste line. 

Occasionally, an over-sized pump will push too much water during backwash and the result will be loss of sand.  As the sand bed diminishes the effectiveness of the sand is reduced.  Simply inspecting the level of the sand once in a while will tell if that is a problem - the solution is to simply control the backwash flow rate.

Paul Wahler, CSP

Did you check your fill water for water balance, and other substances.

could be calcification, or something else that is very high in the fill water.

Salt may not be the best option in your area.  have your water checked.

That's a weird problem. Maybe too much calcium hardness added. I'm not big on salt systems first off all. Anything is suspect. That being said, I've gotten away from sand for years now. Pea gravel above the laterals and Vitro beads are far superior. I'll give an experience of how and why I changed.
Had a customer who had to have his pool converted to Baquacil ( hydrogen peroxide ). He kept his pool at 104 degrees. ( naked girls using it). I had to clean cartridge filter weekly due to high pressure. Replaced it with D.E. Same thing, so a fellow pool man told me about trying a sand filter, with beads. It kept pool sparkling clean and I was able to backwash every 3 months. Now, 1/3rd of my route has been converted. Any nay sayers, try it. I've been servicing pools for 41 years now. Started at Herb's in San Rafael, Ca. ( 5 years) then Geremia's in Sacramento, Ca.( was asked to manage their routes ) but I chose to become a independent pool man. Have trained about seventeen guys, and girls into their own routes. I'm telling you this, to emphasize that beads are the best thing I've discovered in years and don't think your problem would happen. I don't have any other clues about your problem. Never heard of that happening,


It may be calcite formation, or struvite which is mineral formed between magnesium, ammonium and phosphate which will turn a sand bed into concrete over a period of a few weeks.

From the look of the sand,  there also appears to be bacterium coagulation which leads to mud-balling and channelling of unfiltered water throught the filter bed.

Dear Professionals ,

I would  like just to thank you all for the constructive comments on Sand filter . As always , I do appreciate you all taking the time to teach us some informative lessons . 

Yours Sincerely,


Cindy,  Automatic backwash systems are available only in the commercial market.  Part of the complexity of auto b-w system is that it has to also be intergrated with an auto fill system, or process of backwashing could lower the water level too far and damage the pump..  Pac-Fab (Pentair) tried to get one into the residential market many, many years ago and it went nowhere.  

There was a mention in this thread of "rinse" not being  well known.  I have found that the lack of using 'rinse' when backwashing a sand filter is the #1 mistake by poolowners and professionals alike.   Yes, you can skip the 'rinse' step if you backwash for a long enough time, but most people are too impatient or the water level gets too low.  So use the 'rinse' step  and avoid putting dirty water back into the pool.  


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