Pool & spa
HTH / Fi-Clor Rapidfloc / Granular Floc dupe
Why pay around £12.99 for HTH / Fi-Clor? The bulk active is Aluminium sulphate (alum) crystals 17% — 77% less per working litre than a typical shelf pack.
From the retail pack to the active and the mix
1 · Retail
HTH / Fi-Clor Rapidfloc / Granular Floc
1 kg tub · £12.99 typical snapshot
None (alum crystals)
2 · Active
Aluminium sulphate
99% on the label
10043-01-3Al2(SO4)3
Bulk Aluminium sulphate (alum) crystals 17%
3 · Mix
0.025 g/L (25 g/m³ after a shock, vacuum to waste)
£0.00 per working litre · 77% less than the shelf pack
- Active
- Aluminium sulphate
- CAS
- 10043-01-3
- Dupe
- Aluminium sulphate (alum) crystals 17%
- Saving
- 77% / 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
“Clears cloudy water by dropping fines to the floor”
The chemical reality
Floc is alum. Aluminium sulphate is a water-works coagulant sold in 5–25 kg sacks. A 1 kg spa tub is a labelled scoop from that sack. Not a sand-filter magic potion, and not polyquat. Vacuum to waste after it drops.
Active vs filler
99% Aluminium sulphate · 1% carrier / filler — None (alum crystals)
- Typical retail
- £12.99
- 1 kg tub
- Estimated active cost
- £2.40
- Scaled from bulk £12.00 / 5 kg
- Indicative markup
- 5.4×
- Snapshot maths, not a live shop price
The Marketing Claim & The Catch
A 1 kg tub pack of HTH / Fi-Clor Rapidfloc / Granular Floc typically retails around £12.99 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: Clears cloudy water by dropping fines to the floor; and No pre-dissolving on some liquid SKUs — granules are the same alum.
The catch: Floc is alum. Aluminium sulphate is a water-works coagulant sold in 5–25 kg sacks. A 1 kg spa tub is a labelled scoop from that sack. Not a sand-filter magic potion, and not polyquat. Vacuum to waste after it drops.
- “Clears cloudy water by dropping fines to the floor”
- “No pre-dissolving on some liquid SKUs — granules are the same alum”
Proprietary Blend & Dosage Breakdown
The labelled active is Aluminium sulphate at 99%. Everything else in the pack is none (alum crystals).
Even when the pack is sold as “pure” or ready-to-use, the dose that actually does the work is Aluminium sulphate. 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% Aluminium sulphate (alum) crystals 17%, mixed to 0.025 g/L (25 g/m³ after a shock, vacuum to waste).
- Labelled active
- Aluminium sulphate
- 99%
- Carrier
- None (alum crystals)
- Retail pack
- 1 kg tub · £12.99
The Active Chemical Alternative (Dupe Stack)
The dupe stack is Aluminium sulphate (alum) crystals 17% at 99% bulk. Indexed as CAS 10043-01-3, formula Al2(SO4)3. Buy it as 5 kg for around £12.00 from Amazon UK.
Working strength: 0.025 g/L (25 g/m³ after a shock, vacuum to waste). Indicative cost £0.00 per diluted litre — 77% 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.
- Acidic dust. Gloves and goggles. Predissolve in a bucket of pool water. Not for cartridge or DE filters as a filter-aid without the supplier note.
- A typical drop-out dose is about 25 g per cubic metre. Stop the pump, let the floc settle overnight, vacuum to waste.
- pH should be near 7.2–7.6 or alum will not drop cleanly. Test, then floc — do not guess.
- 5 kg treats about 200 m³ at 25 g/m³. A 1 kg branded tub is 40 m³.
Dilution recipe
10,000 L pool / spa volume
Working strength 0.025 g/L (25 g/m³ after a shock, vacuum to waste). Educational estimate from the listed ratio — check the SDS before you mix.
Chemical
250 grams
Aluminium sulphate (alum) crystals 17%
Water
10,000 litres
Carrier / diluent
0% concentrate · 100% water by working volume (solids are dissolved into the water share).
Required PPE
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Side-by-Side Price & Potency Comparison
Head-to-head comparison
| Measure | Retail brandedHTH / Fi-Clor | Raw active dupeDupeStack |
|---|---|---|
| Product | Rapidfloc / Granular FlocAmazon UK search — listing, not a confirmed seller | Aluminium sulphate (alum) crystals 17% |
| Pack / unit | 1 kg tub · £12.99 | 5 kg · £12.00 |
| Active | Aluminium sulphate at 99%Carrier: None (alum crystals) | 99% bulkAl2(SO4)3 |
| CAS number | Not disclosed on pack | 10043-01-3 |
| Working strength | Ready-to-use pack | Dilute 0.025 g/L (25 g/m³ after a shock, vacuum to waste) |
| Cost per litre | £12.99 / pack | £0.00 / L mixed from bulk |
| Headline saving | Baseline | 77% cheaper |
| COSHH / PPE | Follow the branded SDS | Gloves. Chemical-resistant gloves (nitrile or neoprene)Eye protection. Indirect-vent splash goggles — not ordinary spectacles |
Active ingredient and cheaper alternative — FAQ
What is the active ingredient in HTH / Fi-Clor?
HTH / Fi-Clor Rapidfloc / Granular Floc is labelled as Aluminium sulphate at 99%. The carrier is None (alum crystals). Pack size: 1 kg tub. The bulk equivalent we index is Aluminium sulphate (alum) crystals 17% (CAS 10043-01-3).
Is Aluminium sulphate (alum) crystals 17% safe on the intended surface?
Used at the listed working strength (0.025 g/L (25 g/m³ after a shock, vacuum to waste)), 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 HTH / Fi-Clor Rapidfloc / Granular Floc?
Yes. The bulk equivalent is Aluminium sulphate (alum) crystals 17% (CAS 10043-01-3). Indicative saving 77% per working litre versus a pack that typically retails around £12.99. Working strength: 0.025 g/L (25 g/m³ after a shock, vacuum to waste). Live shop prices move.
How do you mix the Rapidfloc / Granular Floc dupe stack?
Acidic dust. Gloves and goggles. Predissolve in a bucket of pool water. Not for cartridge or DE filters as a filter-aid without the supplier note. A typical drop-out dose is about 25 g per cubic metre. Stop the pump, let the floc settle overnight, vacuum to waste. pH should be near 7.2–7.6 or alum will not drop cleanly. Test, then floc — do not guess. 5 kg treats about 200 m³ at 25 g/m³. A 1 kg branded tub is 40 m³.
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.
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More teardowns
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- Retail pack
- £11.501 kg bottle
- Raw active
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- Retail pack
- £9.991.5 kg
- Raw active
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- Retail pack
- £42.005 kg
- Raw active
- TCCA 90% chlorine tablets (200 g)87-90-1
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£24.50Save 77% / L
Indicative DIY stack