Consumer advocacy teardown
Chlorine / Bromine Reducer alternative & active ingredient dupe
Stop paying £16.50 for Fi-Clor / Swimfresh. The bulk active is Sodium thiosulphate pentahydrate (chlorine reducer) — 65% less per working litre than a typical pack.
- Active
- Sodium thiosulphate
- CAS
- 7772-98-7
- Dupe
- Sodium thiosulphate pentahydrate (chlorine reducer)
- Saving
- 65% / L
Saving is per litre of working-strength mix versus a typical pack price, not versus the DIY kit total. Shop prices move — always check the listing.
The Marketing Claim & The Catch
A typical 2.5 kg tub pack of Fi-Clor / Swimfresh Chlorine / Bromine Reducer is about £16.50 in pool & spa. That is a snapshot, not a live Amazon price — listings, sizes and deals move. The marketing line is that you are buying a finished lifestyle product, not a weighed chemical.
On the pack: Neutralises excess chlorine after a shock so you can swim sooner; and No need to waste heated water.
The catch: The spa-shop ‘chlorine reducer’ is photographer’s hypo: sodium thiosulphate. A 2.5 kg tub is a small bag of the 5 kg photo/pool salt. Dose from a test kit. Too much and you will have no sanitiser left.
- “Neutralises excess chlorine after a shock so you can swim sooner”
- “No need to waste heated water”
Proprietary Blend & Dosage Breakdown
The labelled active is Sodium thiosulphate at 99%. Everything else in the pack is none (pentahydrate or anhydrous powder).
Even when the pack is sold as “pure” or ready-to-use, the dose that actually does the work is Sodium thiosulphate. The rest is how they get it into a bottle you will pick up.
Branded working strength is whatever comes out of the bottle. The bulk alternative is 99% Sodium thiosulphate pentahydrate (chlorine reducer), mixed to 0.003 g/L (about 3 g/m³ per ppm to knock down — titrate).
- Labelled active
- Sodium thiosulphate
- 99%
- Carrier
- None (pentahydrate or anhydrous powder)
- Retail pack
- 2.5 kg tub · £16.50
The Active Chemical Alternative (Dupe Stack)
The dupe stack is Sodium thiosulphate pentahydrate (chlorine reducer) at 99% bulk. Indexed as CAS 7772-98-7, formula Na2S2O3·5H2O. Buy it as 5 kg for about £11.50 from Amazon UK.
Working strength: 0.003 g/L (about 3 g/m³ per ppm to knock down — titrate). Indicative cost £0.00 per diluted litre — 65% below a typical branded pack on a per-litre basis, before you reuse leftover bulk.
Follow the mixing method and the supplier SDS. Wear the listed PPE. Do not mix incompatible oxidisers, acids or ammonia.
- Gloves. Predissolve. Never mix dry with oxidisers in a bucket — that is a heat hazard.
- Test free chlorine first. A starting correction is on the order of 3 g per cubic metre per ppm you want to remove. Retest. Do not dump the tub.
- 5 kg is a season of corrections for a domestic pool. A 2.5 kg branded tub is half of that at spa-shop money.
- If you overshoot, you have no sanitiser. Shock back. This is not a substitute for waiting overnight after a modest shock.
Mixing desk
Dilution calculator
Switch between filling a sprayer and covering a measured surface. Figures are educational estimates from the listed ratio — always check the SDS.
Formula
Sodium thiosulphate pentahydrate (chlorine reducer)
- Concentrate
- 30 g
- grams of solid
- Water
- 10,000 L
- carrier volume
- Batch cost
- £0.07
- 10,000 L working solution
- Saved vs retail
- £0.13
- 65% · retail £0.20
Estimated coverage at the listed rate: 8.3 m².
Side-by-Side Price & Potency Comparison
Head-to-head comparison
| Measure | Retail brandedFi-Clor / Swimfresh | Raw active dupeDupeStack |
|---|---|---|
| Product | Chlorine / Bromine ReducerAmazon UK search — listing, not a confirmed seller | Sodium thiosulphate pentahydrate (chlorine reducer) |
| Pack / unit | 2.5 kg tub · £16.50 | 5 kg · £11.50 |
| Active | Sodium thiosulphate at 99%Carrier: None (pentahydrate or anhydrous powder) | 99% bulkNa2S2O3·5H2O |
| CAS number | Not disclosed on pack | 7772-98-7 |
| Working strength | Ready-to-use pack | Dilute 0.003 g/L (about 3 g/m³ per ppm to knock down — titrate) |
| Cost per litre | £16.50 / pack | £0.00 / L mixed from bulk |
| Headline saving | Baseline | 65% cheaper |
| COSHH / PPE | Follow the branded SDS | Gloves. Chemical-resistant gloves (nitrile or neoprene) |
Active ingredient and cheaper alternative — FAQ
What is the active ingredient in Fi-Clor / Swimfresh?
Fi-Clor / Swimfresh Chlorine / Bromine Reducer is labelled as Sodium thiosulphate at 99%. The carrier is None (pentahydrate or anhydrous powder). Pack size: 2.5 kg tub. The bulk equivalent we index is Sodium thiosulphate pentahydrate (chlorine reducer) (CAS 7772-98-7).
Is Sodium thiosulphate pentahydrate (chlorine reducer) safe on the intended surface?
Used at the listed working strength (0.003 g/L (about 3 g/m³ per ppm to knock down — titrate)), the dupe is the same chemistry as the branded pack for pool and spa water once dosed from a test kit. That is not a blanket all-clear: read the supplier SDS, wear the listed PPE, keep acids away from hypochlorite, and follow UK HSE/COSHH rules. Wellness teardowns are supplements, not medicines.
Is there a cheaper alternative to Fi-Clor / Swimfresh Chlorine / Bromine Reducer?
Yes. The bulk equivalent is Sodium thiosulphate pentahydrate (chlorine reducer) (CAS 7772-98-7). Indicative saving 65% per working litre versus a typical £16.50 pack. Working strength: 0.003 g/L (about 3 g/m³ per ppm to knock down — titrate). Live shop prices move.
How do you mix the Chlorine / Bromine Reducer dupe stack?
Gloves. Predissolve. Never mix dry with oxidisers in a bucket — that is a heat hazard. Test free chlorine first. A starting correction is on the order of 3 g per cubic metre per ppm you want to remove. Retest. Do not dump the tub. 5 kg is a season of corrections for a domestic pool. A 2.5 kg branded tub is half of that at spa-shop money. If you overshoot, you have no sanitiser. Shock back. This is not a substitute for waiting overnight after a modest shock.
DupeStack provides chemical concentration data and educational mixing guides. Always review official manufacturer Safety Data Sheets (SDS) and comply with UK Health and Safety Executive (HSE) and COSHH regulations when handling concentrated substances. Some links on this site are affiliate links.
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£23.50indicative kit · Amazon cannot add a mixed search kit as one basket