Pool & spa
Fi-Clor / Swimfresh Chlorine / Bromine Reducer dupe
Why pay around £16.50 for Fi-Clor / Swimfresh? The bulk active is Sodium thiosulphate pentahydrate (chlorine reducer) — 65% less per working litre than a typical shelf pack.
From the retail pack to the active and the mix
1 · Retail
Fi-Clor / Swimfresh Chlorine / Bromine Reducer
2.5 kg tub · £16.50 typical snapshot
None (pentahydrate or anhydrous powder)
2 · Active
Sodium thiosulphate
99% on the label
7772-98-7Na2S2O3·5H2O
Bulk Sodium thiosulphate pentahydrate (chlorine reducer)
3 · Mix
0.003 g/L (about 3 g/m³ per ppm to knock down — titrate)
£0.00 per working litre · 65% less than the shelf 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.
Label teardown
What the pack promises versus what the label chemistry actually is.
The marketing claim
“Neutralises excess chlorine after a shock so you can swim sooner”
The chemical reality
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.
Active vs filler
99% Sodium thiosulphate · 1% carrier / filler — None (pentahydrate or anhydrous powder)
- Typical retail
- £16.50
- 2.5 kg tub
- Estimated active cost
- £5.75
- Scaled from bulk £11.50 / 5 kg
- Indicative markup
- 2.9×
- Snapshot maths, not a live shop price
The Marketing Claim & The Catch
A 2.5 kg tub pack of Fi-Clor / Swimfresh Chlorine / Bromine Reducer typically retails around £16.50 in pool & spa. That is a UK shelf-price snapshot for the maths on this page — not a live shop quote or a manufacturer RRP. 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 around £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.
Dilution recipe
10,000 L pool / spa volume
Working strength 0.003 g/L (about 3 g/m³ per ppm to knock down — titrate). Educational estimate from the listed ratio — check the SDS before you mix.
Chemical
30 grams
Sodium thiosulphate pentahydrate (chlorine reducer)
Water
10,000 litres
Carrier / diluent
0% concentrate · 100% water by working volume (solids are dissolved into the water share).
Required PPE
Loading calculator…
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 pack that typically retails around £16.50. 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 only. Wellness pages compare food supplements, not medicines or prescribed treatments. Always review the supplier Safety Data Sheet (SDS) and comply with UK Health and Safety Executive (HSE) and COSHH regulations when handling concentrated substances. Mixing and storage are at your own risk. Some links are affiliate advertisements (Amazon Associates, eBay Partner Network, and Awin when those programmes are live). Commissions do not change listed concentrations or calculator output.
Related guides
Pool guide
Pool shock, bromine, floc and algaecide — not the same tub
Cal-hypo shock, dichlor granules, MPS oxidiser, BCDMH bromine, alum floc, copper algicide and thiosulphate reducer are different salts. Match the job before you buy a spa-shop tub.
Pool guide
Pool and spa basics: pH, chlorine and cyanuric acid without the brand kit
What Clearwater-style pH Plus, pH Minus, chlorine and CYA actually are — soda ash, dry acid, TCCA and stabiliser — with links to DupeStack teardowns.
Pool guide
Phosphate remover and polyquat — not a shock, and not copper
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More teardowns
Pool & spa
Clearwater pH Plus Spa / Pool Balancer
Clearwater
- Retail pack
- £11.501 kg bottle
- Raw active
- Dense soda ash (sodium carbonate 99%)497-19-8
pH Plus is dense soda ash — 99% sodium carbonate, CAS 497-19-8. Pool-shop packaging turns a £2.70/kg commodity into an £11.50/kg ritual.
Pool & spa
Clearwater pH Minus
Clearwater
- Retail pack
- £9.991.5 kg
- Raw active
- Sodium bisulphate (dry acid)7681-38-1
pH Minus is dry acid — sodium bisulphate. Pool retail is a small tub; chemical suppliers sell it in 5 kg lots for a third of the per-kilo price.
Pool & spa
Clearwater Multifunction Chlorine Tablets
Clearwater
- Retail pack
- £42.005 kg
- Raw active
- TCCA 90% chlorine tablets (200 g)87-90-1
The tablet is 90% TCCA — the same stabilised chlorine used in bulk 200 g pucks. ‘Multifunction’ is a pinch of clarifier and a lot of packaging. Buy TCCA, dose from an SDS, and keep cyanuric acid in range.
£23.50Save 65% / L
Indicative DIY stack