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We are using Aluminum Sulphate as flocculant for the pools we service.

I am working on documenting dosage guides for all our products, As I am not able to find any information I would really appreciate guideline on dosage and methods for Aluminum Sulphate. 

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DIN 19643-2 specifies that the pH be in the range of 6.5 to 7.2 if aluminum salts are used for coagulation or between 6.5 and 7.5 if iron salts are used.  The minimum quantity of coagulant added shall be 0.05 g/m^3 (same as mg/L or ppm) for aluminum salts (expressed as Al) and 0.1 g/m^3 for iron salts (expressed as Fe).

The actual dosage, which is higher than these minimums, is dependent on whatever is necessary to achieve the coagulation goals.  A typical dosage is between 4 and 8 pounds of aluminum sulfate tetradecahydrate per 10,000 gallons (roughly 2-4 pounds aluminum sulfate anhydrous) which translates into 2.2 to 4.4 mg/L Al and you would typically lower the pH to 7.0 before adding the floc.  Typical dosage labels on aluminum sulfate products usually say 2 pounds per 10,000 gallons so you can start there if you like (different products have different aluminum sulfate content so you should follow label instructions).  Also, the adjusted TA (carbonate alkalinity) should be at least 75 ppm.

Hi Richard

Thank you very much for your advise. We buy the aluminum sulphate in bulk and I have therefore never seen a commercial dosage label.

From your answer I understand there there are two types of Aluminum Sulphate, tetradecahydrate and anhydrous. I will find out what type we are using and dose accordingly.

Again thanks alot

There's even more forms than that with different amounts of hydrate (water), but most probably are hydrated so the rough amounts I gave should be OK.  I'd just start with 2 pounds per 10,000 gallons and see how it goes.  Just remember to lower the pH to 7.0 or so since that's very important.

Dear Prof. Falk ,

 I always fully appreciate you for sharing your invaluable knowledge with us . Thank you for this dedication and generosity .

With regard to the topic, I would like to request your attitude towards PAC ( Poly aluminum chloride ) in place for Aluminum sulphate . Thus, i was wonder if you could mind stating your views on it ,and whether it is best practice to use PAC in swimming pool or not .

Thank you in advance for your time and honorable support ,

I look forward to hearing from you ,

Yours Sincerely,



I'm far from being an expert in this area of using floc.  I'm not a professor (and no PhD).  I have seen that people use PAC successfully, but don't have an opinion of PAC vs. aluminum sulfate hydrate (alum).  If you do a Google search, you'll run into some interesting documents describing differences:

Note that there are incompatibilities such as between Alum and PACL.  You'll see that some flocs only work at quite low pH (such as alum) while others are better at more neutral pH.  The only way to know if a water with unknown contaminants will work with a given floc is to do a jar test.

Of course, if you are just talking about swimming pools, then typically the clearing that is needed is either from algae or from suntan lotion and other oils.  The polymeric flocs such as OMNI Liquid Floc Plus or BioGuard Power Floc tend to work better with less need for adjustments, but they aren't inexpensive.  Alum is so popular mostly because of its wide availability and lower price, but it's harder to work with given the low pH requirement (and the pH will vary depending on dose since alum is quite acidic).

Just keep in mind that in a properly maintained pool the use of clarifiers and flocculants can usually be avoided.  The reason for their use in DIN 19643 is not for water clarity but rather to physically remove bather waste organics so that they can be more readily filtered and removed so that they do not form as many disinfection by-products and they are only part of a broader system that includes adsorption onto activated carbon.

Generally speaking, good circulation and filtration are what maintain good water clarity.  The use of coagulants for clarity in swimming pools is usually only needed when the particle sizes of the contaminants are too small for the sand filter to capture on its own.

Dear Mr. Falk ,

I do appreciate you for providing me with such an informative lesson . In fact, your valuable support facilitates the path for collecting reliable data on this topic. i profusely thank you for your time and prompt reply.

As regards suntan lotion and body oils , I would like to say that I always see numerous tiny substance over domestic pool where bathers do not pay attention to basic hygienic issues .In this situation, after testing chemical elements of the pools , and adjusting the PH I went to apply Aluminum Solphate . after two days ,I vacuumed the pools and did back washed the sand filters , but I still saw the very small size floating particles over the water .The water clarification was so clear than before .I still have problem with those particles .

In another case, when I use Omin clarifier , there is no sign of those particles ,and it is easier to apply and totally improve the quality of the job . Yes , the price is not affordable to put into practice in most of the projects.

As you stated above , the reason for using clarifiers and flocs is not for water clarity ,but it is for disposing of bather waste organics according to DIN19643. As I always work on domestic projects and bather waste causes tubidity and greasing media of sand filter , shall I apply more PACl to remove the suntan lotion and especificaly by products of cosmetics in water ? 

Surely, I do peruse those treasure documents and follow your infallible advice with alacrity .

I look forward to hearing from you , 

Yours Sincerely,


I didn't mean to imply that clarifers aren't used for water clarity.  I just meant that their use in DIN 19643 is primarily for coagulating purposes for lower disinfection by-products in high bather-load pools.  Clarifiers do tend to keep pool water clear, BUT if you have a problem with water clarity that need clarifiers to help, then you've likely got other problems.  See the following link for 100 Reasons for Cloudy Swimming Pool Water:

The #1 reason for dull/cloudy water is nascent algae growth.  Your Free Chlorine to Cyanuric Acid ratio is likely too low.  To prevent green and black algae growth regardless of algae nutrient (phosphate, nitrate) level, you need the FC/CYA ratio to be at least 7.5%.  If you want to use a lower ratio, then you need to prevent algae growth with supplements.  The use of a phosphate remover can be an economical way to do this, but precludes using any HEDP-based metal sequestrant (such sequestrants should only be used if you indeed have metals in the water -- i.e. iron, copper, manganese).

For surface oils that don't break down fast enough or get sucked to the filter, you can use a sprofanity filter removed this wordball in the skimmer.  For small particles you may see especially at night in front of an underwater pool light you may not have good enough circulation or filtration, particularly if you have a sand filter.  For temporary clearing, you can add some DE through the skimmer to a sand filter or use a filter aid product (you just add enough for a 1-2 PSI rise and you wait 10 minutes or so after adding to look for that rise).  Normally, though, if you have proper circulation and filtration the water should be fairly clear.  If you feel you need to use a clarifier, some good ones include GLB Clear Blue and Bioguard Polysheen Blue.  These are polymeric clarifiers, but not that these are incompatible with polymeric metal sequestrants.

Dear Mr. Falk ,

Thank you for enlightening me about the subject from different angles . The link was excellent for digging deep into chemical of swimming pool water .Your impeccable technical writings are greatly appreciated .

Also, your technical suggestions on removing oils from surface of the pool are perfect and practical .

Once more , thank you for taking your time to teach me unforgettable lessons ,and encouraging to keep learning as much as possible .

Yours Sincerely,



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