Sequestrant - Further Reading

What is a Sequestrant?

Sequestrant is any of several chemicals that bind to metal ions dissolved in the water and prevent them from depositing as stains. All sequestrants break down slowly over time, so you need to add more at regular intervals to replace the portion that has broken down.[1]

What Does a Sequestrant Do?

A metal sequestrant holds onto metals to prevent them from staining pool surfaces. It's only needed if you've got metals (iron, copper, manganese) in your water, such as sometimes occurs in well water.[2]

When Do You Use a Sequestrant?

There is no point in using sequestrants day to day unless you know you have metal problems. The only time sequestrant is worth using as a general protection is when fresh plaster is applied, as metal stains on brand new plaster can never be removed.

Other uses of sequestrant is during an Ascorbic Acid Treatment.

PROTEAM Metal Magic has a Metal Magic Sponge Test to determine if a stain is organic or metallic and the proper does level for the stains.

What are Sequestrant Products?

Sequestrants based on HEDP, phosphonic acid, or phosphonic acid derivatives are the most effective.

The top sequestrants are:

  • ProTeam's Metal Magic
  • Jack's Magic The Pink Stuff (regular)
  • The Blue Stuff (fresh plaster)
  • The Purple Stuff (salt)

You can also find many other brands with similar active ingredients, some of which are noticeably less expensive.

What Chemical is Usually in Seqestrant?

HEDP (Hydroxyethylidene Diphosphonic Acid) is often listed in ingredients as Etidronic acid. It may also be listed as 1-Hydroxyethylidene-1,1-diphosphonic acid.

We don't recommend sequestrants that mix inother chemicals like polymers.

HEDP is an organophosphate metal sequestrant, which is not a nutrient for algae. The Blue/Pink/Purple Stuff can break down into an orthophosphate, which is a nutrient and can cause algae blooms (unless chlorine levels are kept high enough).

What is the Effect of Long Term Use of Sequestrant?

Most sequestrants are HEDP based. Over time the sequestrant breaks down from chlorine exposure into phosphates (it does this no matter what) and that's why you need maintenance dosing. With extended use of HEDP, phosphates will build up in the water. High PO4 levels make it quicker and easier for algae to form if the FC goes below minimum recommended levels. So, with extensive use of sequestrants, you must be mindful to keep your FC/CYA ratio properly maintained as high phosphate water is more reactive to algae than low phosphate water.[3]

Long term usage of sequestrants can effect water chemistry as discussed in this post.

What is the Effect of Chlorine on HEDP Sequestrant?

Jack's said that Blue/Pink/Purple Stuff can withstand around 10 ppm of Free Chlorine (FC) for a short period of time, but higher FC levels, or longer periods of time, will "consume" the HEDP. If there are sequestered metals still in the water, they will be released back into the water.[4]

A SLAM treatment will probably consume all the HEDP in the water, possibly causing staining and requiring that the HEDP residual be built back up.

Can Sequestrant be Filtered?

Jack's said that the combined HEDP-metal molecules will be filtered out of the water by filter media that removes particles 10 microns or smaller in size. This would include D.E. and Zeolite filter media. Coarser filter media, i.e. sand, requires the use of a filter aid like D.E. or fiber. Once the HEDP-metal molecules are trapped in the filter, the filter can be backflushed and the metals physically removed from the pool water.

Does Phosphate Treatment Effect HEDP Sequestrant?

Jack's said that doing a phosphate treatment will not degrade the organophosphate metal sequestrant in Blue/Pink/Purple Stuff. The phosphate treatment will remove the orthophosphates.

Testing for Sequestrant Levels

LaMotte sells a Sequestrant Test Kit (Part No. 4064-01) for less than half the cost of the test kit sold by Jack's ($36-$40 vs. $98). I confirmed that the LaMotte test measures HEDP. The two kits appear very similar.[5]

Some phosphate test kits test for both organophosphate and orthophosphate, and if you are using an organophosphate metal sequestrant this can yield crazy-high readings that don't drop even with a phosphate treatment.

The LaMotte phosphate test kit only tests for orthophosphates.


  • Polymeric metal sequestrants, such as Natural Chemistry® METALfree, are NOT compatibile with Polyquat or with most clarifiers. Natural Chemistry® METALfree is a acrylic copolymer with citric acid.[6]