Consumer advocacy teardown
Rapidfloc / Granular Floc alternative & active ingredient dupe
Stop paying £12.99 for HTH / Fi-Clor. The bulk active is Aluminium sulphate (alum) crystals 17% — 77% less per working litre than a typical 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.
The Marketing Claim & The Catch
A typical 1 kg tub pack of HTH / Fi-Clor Rapidfloc / Granular Floc is about £12.99 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: 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 about £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.
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
Aluminium sulphate (alum) crystals 17%
- Concentrate
- 250 g
- grams of solid
- Water
- 10,000 L
- carrier volume
- Batch cost
- £0.60
- 10,000 L working solution
- Saved vs retail
- £2.65
- 82% · retail £3.25
Estimated coverage at the listed rate: 8.3 m².
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 typical £12.99 pack. 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. 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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DIY stack · 77% / L vs branded
£24.50indicative kit · Amazon cannot add a mixed search kit as one basket