RO Antiscalants: 10 Chemistries, Dosing and Selection

RO antiscalants are threshold scale inhibitors, mainly phosphonates and polymers, that are dosed continuously into reverse osmosis feedwater upstream of the cartridge filter, typically at 2 to 5 mg/L (ppm) of feed as product, to keep calcium carbonate, calcium sulfate (sulphate), barium sulfate, strontium sulfate, calcium fluoride and silica dissolved as recovery concentrates them. A brackish-water RO train runs at up to about 90 % recovery, so the salts in its last elements are concentrated about tenfold. Which chemistry keeps them in solution, at what dose, and how is it proven?

Antiscalants are the one family of water treatment chemicals that exists mainly because of membrane recovery, with RO limits, dose basis and certification rules that set them apart from other water treatment chemicals.

Recovery sets the need, ten chemistries led by ATMP do the work, and the product goes in after acid and before the cartridge filter. Control runs through the concentrate LSI and normalized data; failures come from calcium, gel or biofilm reactions; NSF/ANSI/CAN 60, EN 15040:2014 and discharge permits set the rules.

The four figures that frame an RO antiscalant program are listed below.

• 2 to 5 mg/L (ppm) of feed as product: the typical antiscalant dose (Hydranautics TAB-111).
• 202 companies, 1,582 products and 2,139 product-function rows: NSF/ANSI/CAN 60 listings under the function Reverse Osmosis Antiscalant (NSF listings, 2026-10-21).
• 10 mg/L as product: the most common NSF/ANSI/CAN 60 maximum use level (MUL) for RO antiscalants, on 721 listing lines (same listings).
• 4 times: the salt concentration in the concentrate at 75 % recovery, assuming full salt rejection.

Every value on this page is checked against primary sources; see our methodology and fact-checking process.

What Is an RO Antiscalant and Why Does Reverse Osmosis Need Scale Inhibition?#

Reverse osmosis needs scale inhibition because the membrane rejects 95 to more than 99 % of dissolved salts, so every salt in the feed leaves the last element at several times its feed concentration, and calcium carbonate, sulfates, fluoride and silica pass their solubility limits there. An antiscalant does not take that excess out of the water; it delays precipitation in the concentrate. RO antiscalants fall into 3 classes, sodium hexametaphosphate, organophosphonates and polyacrylates, and Hydranautics Technical Application Bulletin TAB-111 puts the polymers at 2,000 to 10,000 Da.

Threshold inhibition explains why 2 to 5 mg/L suffices: the inhibitor adsorbs onto the growth sites of sub-microscopic crystallites and works far below the stoichiometric dose. Crystal modification and dispersion complete the effect, and the chemistry of threshold inhibition has its own page.

How far above saturation can an antiscalant hold each salt, and what sets the concentration factor? The recovery of the train and the saturation limits that membrane manufacturers publish answer it.

How Does RO Recovery Drive Scale Formation?#

Recovery drives scale formation through the concentration factor, CF = 1/(1 - Y): at 75 % recovery the concentrate carries 4 times the feed salt concentration, at 90 % recovery 10 times. The formula is from the DuPont FilmTec RO and NF Technical Manual (Rev. 20, 2026); rows other than 75 % are calculated, assuming full salt rejection.

The table compares recovery, concentration factor and typical RO application.

The general chemistry of scale formation is the same in boilers, cooling towers and membranes; in RO the concentration factor is the lever.

Feed type decides which scalant limits recovery first. Seawater RO stops at 40 to 50 % recovery, yet the same manual recommends an antiscalant above 35 %, and barium sulfate becomes critical below 15 µg/L barium in seawater against below 5 µg/L in brackish water. Calcium phosphate was uncommon until RO treated municipal wastewater for reuse, where the manual cites tertiary effluent with 6.1 to 12.2 mg/L phosphate and 40 to 64 mg/L calcium.

Which Scales Do Antiscalants Control, and How Far Above Saturation?#

Antiscalants hold 6 scales above saturation: the TAB-111 bulletin reports calcium sulfate up to 400 %, strontium sulfate up to 1,200 %, barium sulfate up to 8,000 % and calcium fluoride up to 12,000 % of saturation, and a concentrate LSI up to +2.9, with antiscalant present.

The same bulletin reports the following maximum saturation values with antiscalant and the levels at which its projection raises an alarm.

Maximum values reported by one membrane manufacturer; the limit for a given product comes from its supplier projection.

The alarm column marks where the projection flags a design, not where scale is certain, and the bulletin calls a concentrate LSI of +1.8 the conservative design value. Which chemistries reach these limits?

Which 10 Chemistries Are Used as RO Antiscalants?#

The 10 chemistries used as RO antiscalants are 4 phosphonates (ATMP, HEDP, DTPMP and PBTC), 3 polycarboxylate polymers (polyacrylates, polymaleic acid and AA/AMPS copolymer), 1 polyphosphate (SHMP) and 2 phosphorus-free green polymers (PASP and PESA), and most commercial products blend two or more of them.

About 85 % of NSF/ANSI/CAN 60 RO antiscalant listing lines fall under blend categories (NSF listings, 2026-10-20), so buyers ask for the active classes and their EN standard. The table compares the 10 chemistries by class, target scales, dose basis, NSF/ANSI/CAN 60 status, strengths and limits.

Dose ranges and MULs are as product. Formulated products blend these chemistries; the MUL on the product listing, not the chemistry, sets the legal ceiling.

1. ATMP: The Most-Listed Phosphonate Antiscalant#

ATMP (amino trimethylene phosphonic acid, CAS 6419-19-8) is the most frequently listed single phosphonate in NSF/ANSI/CAN 60 RO antiscalants, with 166 listing lines, and EPRI ranks the amino-phosphonates among the best calcium sulfate inhibitors used in RO. Its MULs run from 4 to 100 mg/L as product, most often 20 mg/L (NSF listings, 2026-10-20). ATMP is chlorine-sensitive (EPRI 2014), but polyamide RO feed is dechlorinated below 0.1 mg/L free chlorine anyway. ATMP leads the phosphonate scale inhibitors compared across all systems.

2. HEDP#

HEDP (1-hydroxyethylidene-1,1-diphosphonic acid, CAS 2809-21-4) appears in 69 NSF/ANSI/CAN 60 RO antiscalant listing lines and inhibits calcium carbonate, but its calcium salt precipitates first when calcium, pH and dose are all high. Listed HEDP products carry MULs of 0.8 to 80 mg/L as product, most often 20 mg/L (NSF listings, 2026-10-20). In the Amjad and Zuhl laboratory test, HEDP tolerates only 7.5 mg/L at 250 mg/L Ca2+, the lowest of the three common phosphonates.

3. DTPMP: The Sulfate and Barium Specialist#

DTPMP (diethylenetriamine penta(methylene phosphonic acid), CAS 15827-60-8) is the amino-phosphonate chosen for sulfate and barium sulfate scale, with NSF/ANSI/CAN 60 MULs of 3 to 20 mg/L as product (NSF listings, 2026-10-20). It appears in 23 RO listing lines and also inhibits carbonate and phosphate scale. Its limit is purity: impurities supply 38 to 65 % of the total phosphorus in DTPMP antiscalants, against about 20 % in ATMP products. Two related amino-phosphonates list for RO as well: HDTMPA at 5 or 20 mg/L and PAPEMP in one listing at 20 mg/L.

4. PBTC#

PBTC (2-phosphonobutane-1,2,4-tricarboxylic acid, CAS 37971-36-1) tolerates far more calcium than HEDP or ATMP, 73 mg/L at 250 mg/L Ca2+ in the Amjad and Zuhl laboratory test, and carries only 11.5 % phosphorus by mass. Listed PBTC antiscalants carry MULs of 5 to 20 mg/L as product, typically 20 mg/L (NSF listings, 2026-10-20). PBTC is not phosphorus-free: 1 mg/L adds about 0.1 mg/L total phosphorus, against 0.3 mg/L for HEDP (EPRI 2014).

5. Polyacrylic Acid and Sodium Polyacrylate: The Main Polymer Antiscalants#

Polyacrylic acid and its sodium salt are the main polymer antiscalants in RO: together they account for 80 NSF/ANSI/CAN 60 RO antiscalant listing lines, carry no phosphorus, and the high-molecular-weight grades raise the solubility of silica. The acid lists at 2.5 to 100 mg/L and the sodium salt at 1 to 125 mg/L as product (NSF listings, 2026-10-20). In blends, 10 mg/L polyacrylic acid cut HEDP calcium tolerance from 7.5 to 2 mg/L (Amjad and Zuhl). Copolymers and dispersants are grouped with them under polymer scale inhibitors.

6. Polymaleic Acid (HPMA)#

Polymaleic acid (hydrolyzed polymaleic anhydride, HPMA) is a phosphorus-free polycarboxylate listed under NSF/ANSI/CAN 60 for RO and distillation antiscalant use, with MULs of 3 to 20 mg/L as product and 14 of its 21 listing lines at 20 mg/L (NSF listings, 2026-10-20). It holds calcium carbonate at high saturation but tolerates calcium poorly: 10 mg/L polymaleic acid lowered HEDP calcium tolerance from 7.5 to 4.0 mg/L (Amjad and Zuhl).

7. AA/AMPS Sulfonated Copolymer#

AA/AMPS copolymer (acrylic acid / 2-acrylamido-2-methylpropane sulfonic acid, CAS 40623-75-4) adds sulfonate groups that keep calcium phosphonate and calcium phosphate from precipitating where plain polyacrylates and polymaleic acid fail. The sulfonate gives calcium tolerance and dispersion; the carboxylate gives threshold activity. NSF/ANSI/CAN 60 has no dedicated AA/AMPS category, and no stand-alone RO dose is published.

8. Sodium Hexametaphosphate (SHMP): The Legacy Polyphosphate#

Sodium hexametaphosphate (SHMP) is the oldest RO antiscalant, and the DuPont FilmTec RO and NF Technical Manual (Rev. 20, 2026) now calls it generally not recommended because it hydrolyzes to orthophosphate, loses effect and can itself form calcium phosphate scale. The same manual still accepts a concentrate LSI below 1 with 20 mg/L SHMP in the concentrate, a concentrate value rather than a feed dose. SHMP (CAS 68915-31-1) is standardized as ANSI/AWWA B502-23 and, as a membrane antiscalant, under EN 15041.

9. Polyaspartic Acid (PASP): A Green, Phosphorus-Free Option#

Polyaspartic acid (PASP) is a phosphorus-free polyamino acid that inhibited 95 % of calcium carbonate and 90 % of calcium sulfate at 5 mg/L in static laboratory tests (Liu et al. 2011), but it has no NSF/ANSI/CAN 60 chemical category (NSF search, 2026-10-20). The 5 mg/L is a test concentration, not an RO dose, and thermal stability limits the unmodified polymer. PASP and PESA are compared with other green and phosphorus-free scale inhibitors.

10. Polyepoxysuccinic Acid (PESA)#

Polyepoxysuccinic acid (PESA) is a phosphorus- and nitrogen-free polycarboxylate studied mainly for calcium fluoride scale, where a modified PESA reached about 100 % inhibition at 200 mg/L in a static research test, a concentration far above any RO dose. PESA has no NSF/ANSI/CAN 60 chemical category (NSF search, 2026-10-20), and claims of good biodegradability rest on vendor statements without test data.

How Is an RO Antiscalant Program Designed and Dosed?#

An RO antiscalant program is designed in 4 steps: a projection run on the feedwater analysis chooses the product and dose, the injection point is fixed upstream of the cartridge filter, the dose is set on feed flow as product, and a metering pump interlocked with the feed pump doses it continuously.

How Do You Choose an RO Antiscalant? Projection Software and Supplier Tests#

The best RO antiscalant for a plant is the product whose projection, run on that plant's feedwater analysis, recovery and temperature, holds every scalant below its limit at the lowest dose, and that has passed the membrane maker's compatibility test. Membrane makers' design programs and supplier projection programs run that calculation; buyers should ask for the printout, not only the product name.

Hydranautics Technical Application Bulletin TAB-111 lists 7 questions to put to an antiscalant supplier.

• Membrane compatibility, confirmed by the membrane manufacturer.
• Reference plants with more than 1,000 hours on the product.
• Reactions with iron, other metals and cationic polymers.
• Recommended and maximum dose.
• Solubility limits reached for each scalant.
• Discharge restrictions on the concentrate.
• Suitability for potable water production.

The DuPont FilmTec RO and NF Technical Manual (Rev. 20, 2026) adds a compatibility test of at least 1,000 hours on spiral elements after a 12-hour baseline, and a one-month biogrowth test at 1, 6, 10 and 25 % dilutions with weekly plate counts.

Where Is Antiscalant Injected? After Acid and Dechlorination, Before the Cartridge Filter#

Antiscalant is injected into the RO feed upstream of the cartridge filter and downstream of the acid injection point and its mixing zone, so the filter protects the membrane from any precipitate formed at the dosing point. The bulletin sets this order; the antiscalant never goes in after the cartridge filter.

The manual lists the online chemical sequence of an RO plant in 8 steps.

1. Oxidant (chlorination) at the intake.
2. Coagulant and flocculant.
3. Media or membrane filtration.
4. Sodium bisulfite (SBS) for dechlorination.
5. Acid for pH and LSI control.
6. Antiscalant.
7. Cartridge filter, 5 µm recommended, below 10 µm absolute, replaced at least every 3 months.
8. High-pressure pump.

Dechlorination comes first because polyamide tolerates less than 0.1 mg/L free chlorine; sodium metabisulfite (SMBS) needs 1.34 mg per mg chlorine in theory and 3.0 mg in practice (same manual), as detailed under dechlorination chemicals.

How Much Antiscalant? Dose Basis and Dosage Arithmetic#

RO antiscalant is dosed at 2 to 5 mg/L (ppm) of feed water, stated as product, according to the bulletin, and the projection sets the exact value from the feed analysis and recovery. A published supplier range runs 0.5 to 4 mg/L, while 85 % of NSF/ANSI/CAN 60 MULs sit at or below 20 mg/L, median 12 to 13 mg/L as product (NSF listings, 2026-10-20).

The worked example below converts a dose into a daily product feed, with every input labelled.

• Feed flow: 100 m³/h (440 gpm).
• Dose: 3 mg/L as product.
• Formula: kg/d = mg/L x m³/h x 0.024; lb/day = mg/L x MGD x 8.34.
• Result: 300 g/h, or 7.2 kg/d (15.9 lb/day) of product.
• Active basis: with a 50 % ATMP liquid, 3 mg/L of product is about 1.5 mg/L of active ATMP.
• Concentrate at 75 % recovery: about 12 mg/L, a consequence of the dose, never the dose itself.

RO doses and MULs are stated as product, cooling-tower phosphonate doses as active. The same dosage arithmetic for any flow and purity runs in the dosage and feed rate calculator.

Continuous Feed, Dosing Pumps and Dilution#

Antiscalant is fed continuously, never as a slug, by a metering pump that strokes at least once every 5 seconds and is interlocked with the RO feed pump, so the membrane never sees unprotected concentrate. The four feed rules are listed below.

An antiscalant dosing system is therefore small: a day tank, a metering pump, an injection quill and the interlock. Pump types and sizing for dosing pumps are covered on chemical dosing pumps.

How Is Antiscalant Performance Controlled and Tested?#

Antiscalant performance is controlled on paper by the concentrate saturation indices of the projection and in operation by normalized permeate flow, salt passage and pressure drop.

LSI and S&DSI of the Concentrate#

The concentrate LSI decides how much work an antiscalant must do: the DuPont FilmTec RO and NF Technical Manual (Rev. 20, 2026) requires LSIc below 0 without antiscalant, below 1 with 20 mg/L SHMP in the concentrate, and allows values above 1 only with polymeric inhibitors at the supplier's stated limit. Hydranautics TAB-111 targets a concentrate LSI of -0.2 with acid alone, and the manual notes that concentrate pH usually runs about 0.5 units above feed pH.

ASTM D3739-19 applies the LSI to concentrate of 10 to 10,000 mg/L TDS and ASTM D4582-23 the Stiff and Davis index above that; the method is worked through on the Langelier saturation index (LSI) page.

The manual's criteria fall into 3 cases.

• LSIc below 0: no antiscalant needed for calcium carbonate.
• LSIc below 1: acceptable with 20 mg/L SHMP in the concentrate.
• LSIc above 1: polymeric inhibitors only, at the supplier's limit.

The worked example shows how acid moves a brackish concentrate between those cases (calculated from the manual's method, pK1 6.35 at 25 °C assumed).

With an antiscalant whose projection allows it, the plant runs the untreated +1.46; acid alone needs 98 mg/L sulfuric acid to pass the -0.2 target.

Sulfate, Fluoride, Phosphate and Silica Saturation#

Sulfate, fluoride, phosphate and silica scales are checked as ion products against solubility products: the manual adjusts the design when the concentrate ion product of calcium sulfate exceeds 0.8 Ksp, and barium sulfate becomes critical at barium feed levels as low as 5 µg/L in brackish water. The 4 non-carbonate checks are listed below.

• Calcium and strontium sulfate: design change at an ion product above 0.8 Ksp.
• Barium sulfate: critical from 15 µg/L barium in seawater and 5 µg/L in brackish water.
• Calcium fluoride: scaling possible from 0.1 mg/L fluoride when calcium is high.
• Calcium phosphate and silica: low feed pH controls phosphate; amorphous silica dissolves to typically 100 to 150 mg/L near neutral pH.

Only high-molecular-weight polyacrylates raise silica solubility, and the bulletin alarms at 100 %; pH and temperature limits are covered under silica scale in RO.

Normalized Data, Cleaning Triggers and SDI#

Normalized data show whether the antiscalant is working: scaling appears first as a rising pressure drop and falling normalized permeate flow in the tail elements, while biofouling shows at the lead end (same manual). ASTM D4516-19a standardizes the normalization of RO performance data.

Cleaning is triggered by the normalized data in the table below, and carbonate scale and metal oxides go with the acid cleaners described under RO membrane cleaning chemicals.

Antiscalants do not change particle fouling, which is measured as the silt density index (SDI) under ASTM D4189-23, with SDI15 at or below 5 required and below 3 recommended (same manual).

What Goes Wrong: Antiscalant Failure Modes and Membrane Fouling#

RO antiscalant programs fail in 4 ways: the inhibitor precipitates with calcium, it reacts with iron, aluminum or a cationic polymer into a gel, its phosphorus impurities feed biofilm, or a polyphosphate hydrolyzes and the concentrate scales after shutdown.

The DuPont FilmTec RO and NF Technical Manual (Rev. 20, 2026) defines 4 kinds of membrane fouling: colloidal, biological, organic and scaling. Scale is one of the 4 kinds of membrane fouling, and the antiscalant failures below create the other kinds too.

Calcium Phosphonate Precipitation and Overfeed#

Overfeeding a phosphonate antiscalant into a hard, high-pH concentrate can precipitate the inhibitor itself as a calcium phosphonate, and the Amjad and Zuhl tests show the margin: at 250 mg/L Ca2+, pH 9.0 and 45 °C, HEDP tolerates only 7.5 mg/L, ATMP 13.5 mg/L and PBTC 73 mg/L. At 750 mg/L Ca2+ these fall to 4.8, 7.0 and 50 mg/L, and moving from 25 to 60 °C (77 to 140 °F) lowers them 1.5 to 2 times. These are laboratory cooling-water conditions, not RO dose limits. Sulfonated copolymers such as AA/AMPS prevent calcium phosphonate precipitation where plain polyacrylates fail.

Iron, Aluminum and Cationic Polymer Gels: Prevention and EDTA Cleaning#

Iron, aluminum and cationic polymers turn an anionic antiscalant into a gum-like gel on the membrane that, per the technical manual, only repeated alkaline EDTA cleaning removes, so the first defense is keeping Fe3+ and aluminum below 0.05 mg/L in the RO feed and using anionic or nonionic flocculants upstream. The manual prefers in-line ferric coagulant at 10 to 30 mg/L and does not recommend aluminum ahead of RO; cationic polyacrylamide flocculants carried over from pretreatment are the classic trigger.

The DuPont FilmTec Cleaning Procedures manual (Form 45-D01696, Rev. 13, 2026) sets the alkaline chelant clean at 0.1 wt % NaOH with 1.0 wt % Na4EDTA at pH 12 and 35 °C (95 °F) maximum. Concentrations and pH for alkaline cleaning with EDTA are on the EDTA page.

Biofouling Fed by Phosphonate Impurities#

Phosphonate antiscalants can feed biofilm because their impurities supply phosphorus: in one analysis of 24 technical antiscalants, impurities made up about 20 % of total phosphorus in ATMP and PBTC products and 38 to 65 % in DTPMP products. The same analysis found AMPA at 1.9 to 157 mg/L in the products. A separate review finds the effect formulation-specific: antiscalants can stimulate growth through orthophosphate and labile organics, or inhibit it by sequestering iron.

Biofilm forms 3 to 5 days after inoculation in biologically active feed (technical manual). Biocides and nutrient limits belong to membrane biofouling control.

Hydrolysis, Shutdown Flushing and Preservation#

Every RO shutdown on an antiscalant program starts with a flush, which the technical manual makes mandatory when antiscalants are used, because concentrate left standing in the elements stays supersaturated. Polyphosphate adds a second risk: SHMP hydrolyzes to orthophosphate, so a stale day tank loses inhibition and gains calcium phosphate potential.

Shutdowns longer than 48 hours need preservation, typically 1 to 1.5 % SMBS in place (technical manual), covered under RO membrane preservation.

Which Rules Apply to RO Antiscalants?#

Three sets of rules apply to RO antiscalants: NSF/ANSI/CAN 60 when the permeate is drinking water in the US and Canada, the EN membrane-antiscalant standards under the EU Drinking Water Directive, and discharge permits for the concentrate that carries the antiscalant.

NSF/ANSI/CAN 60 for Potable RO#

An antiscalant dosed into an RO system that makes drinking water is certified to NSF/ANSI/CAN 60 under the product function Reverse Osmosis Antiscalant, which listed 202 companies, 1,582 products and 2,139 product-function rows on 2026-10-21, with product-specific maximum use levels, most often 10 mg/L as product. The next values are 20 mg/L (424 lines) and 15 mg/L (264 lines) (NSF listings, 2026-10-21). The requirement comes from the states: 49 US states require the standard through legislation, regulations or policies (NSF survey of ASDWA members).

Section 8 of the standard covers membrane antiscalants, and MULs are explained under NSF/ANSI/CAN 60. Three rules make an MUL binding, as listed below.

• Total across the train: the MUL limits the dose from all application points together.
• Label and listing: the MUL appears on the label or shipping documents and on the listing.
• Lapse: certification lapses when the product is repackaged, diluted, blended or reacted at an uncertified site.

Thermal desalination plants use the function Distillation Antiscalant: 75 companies, 333 products and 428 product-function rows (NSF listings, 2026-10-21).

EN 15039, EN 15040 and EN 15041 Under the EU Drinking Water Directive#

In Europe, membrane antiscalants for drinking water are specified by 3 CEN standards, EN 15039 for polycarboxylates, EN 15040:2014 for phosphonates and EN 15041 for polyphosphates, and EN 15040 limits arsenic, cadmium and selenium to 3 mg/kg and lead to 10 mg/kg of dry product. EN 15040:2014 also caps nickel and chromium at 10, antimony at 3 and mercury at 1 mg/kg dry product, and covers ATMP, HEDP, DTPMP (as DETAPMP), PBTC and four further phosphonates. Directive (EU) 2020/2184 places treatment chemicals under Article 12.

These product standards belong to the CEN/TC 164 series listed under EN standards for drinking water treatment chemicals.

Concentrate Discharge, Phosphorus and NPDES Permits#

RO concentrate carries the antiscalant at about the concentration factor times the feed dose, roughly 12 mg/L at 3 mg/L and 75 % recovery, and a phosphonate antiscalant adds phosphorus to that discharge: 0.3 mg/L of total phosphorus for every 1 mg/L of HEDP (EPRI 2014). PBTC adds about 0.1 mg/L per mg/L; polyacrylates and polymaleic acid add none.

In the US, a direct discharge needs a permit under Clean Water Act section 402 and 40 CFR 122, where scale inhibitors are disclosed on the application and controlled through effluent limits and whole effluent toxicity testing under NPDES permits.

Phosphonates leave treatment plants by sorption to sludge, not biodegradation (Nowack 1998, Water Research), and dense desalination brine can spread up to 5 km, carrying antiscalants.

Where concentrate goes to a municipal sewer, its phosphorus counts against chemical phosphorus removal targets.

How Do RO Antiscalants Fit into the Full Reverse Osmosis Chemical Program?#

The antiscalant is one of the online chemicals of an RO plant, next to coagulants and flocculants, chlorination and dechlorination, acid and biocides, while cleaners and preservatives are used off-line.

The full set of reverse osmosis and membrane chemicals is mapped on the membrane hub, online and off-line.

Flux, rejection and staging, the process facts behind the numbers above, are explained under how reverse osmosis works.

Antiscalant Versus Acid Feed, Softening and Other RO Pretreatment#

Acid feed lowers the concentrate LSI by converting alkalinity to carbon dioxide, and the DuPont FilmTec RO and NF Technical Manual (Rev. 20, 2026) lists acid and/or antiscalant for well water ahead of a 5 µm cartridge filter, while sulfuric acid lowers the barium level at which barium sulfate becomes critical to below 2 µg/L. Seawater RO typically runs about 10 mg/L sulfuric acid to a feed pH of about 7 for a negative S&DSI (same manual). Coagulation, dechlorination and acid feed are planned together under RO pretreatment chemistry.

Sulfuric and hydrochloric acid, the two acids of the LSI example, are compared among acids for pH adjustment.

Antiscalants and Scale Inhibitors in Cooling Towers and Thermal Desalination#

Antiscalant and scale inhibitor name the same molecules, but in cooling towers phosphonate doses are stated as active, while RO antiscalants are dosed and certified as product.

The full family of scale inhibitors is covered across boilers and cooling towers on the hub. Cooling-tower doses as active are HEDP 2 to 5, ATMP 2 to 3 and PBTC 3 to 5 mg/L (Standish 2024), with cycles-based dosing under scale and deposit control in cooling towers.

Boron, bromide and thermal antiscalants are covered under seawater desalination chemicals.

Is antiscalant toxic?#

Concentrated antiscalant products are corrosive or irritant acids to handle, while at dosing level a drinking-water antiscalant is assessed for health effects at its maximum use level under NSF/ANSI/CAN 60. ECHA notified classifications list HEDP for serious eye damage (H318) and harm if swallowed (H302), and ATMP for eye irritation (H319) and metal corrosion (H290); the supplier SDS gives each product's label.

Does antiscalant reduce TDS?#

No: an antiscalant keeps scaling salts dissolved so that the membrane can go on rejecting them, and the TDS reduction of 95 to more than 99 % comes from the RO membrane itself.

Can any antiscalant be used in an RO system?#

No: an RO antiscalant must be compatible with the membrane (the FilmTec manual tests at least 1,000 hours on spiral elements), anionic products must not meet cationic polymers, iron or aluminum, and drinking-water plants need an NSF/ANSI/CAN 60 listing for the reverse osmosis antiscalant function.

Who Supplies RO Antiscalants and Runs RO Programs?#

RO antiscalants come from 202 companies with NSF/ANSI/CAN 60 listings (NSF listings, 2026-10-21), and most sell blends under trade names, so a request should name the scalants, the recovery and whether NSF/ANSI/CAN 60 certification is needed.

Manufacturer, blender and distributor types are compared under water treatment chemical suppliers. A quote depends on the active classes, required MUL, monthly volume, packaging (drum, IBC or bulk) and delivery country.

Public procurement records show what buyers paid at a given date and place; they include delivery and local terms and are not a current price.

Full-service RO programs are bought from a water treatment program provider.