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pH minus granules buying guide

Updated: 21 October 2026

You have a high reading on a UK test strip, and the basket is full of tubs that all say pH minus. This pH minus granules buying guide is about matching the grams in the tub to the vessel you actually treat, and about refusing a listing whose weight or chemical name does not hold together. Shelf prices below come from the [pH minus comparison](/hub/pool-care/ph-minus) on 19 October 2026. They are this batch on amazon.co.uk, not a cheapest-in-Britain survey. The Products Compared editorial team compared those listings with public notes from BISHTA and PWTAG. We did not lab-test a tub. A qualifying purchase can earn a commission at no extra cost to you.

You have a high reading on a UK test strip, and the basket is full of tubs that all say pH minus.

Our top picks

Zagosa Zagosa pH minus granules, 1.5 kg

Best overall

Zagosa Zagosa pH minus granules, 1.5 kg
6.2/10about £10.95
View offer
Zagosa Zagosa pH minus granules, 5 kg

Rank 2

Zagosa Zagosa pH minus granules, 5 kg
8.1/10about £18.25
View offer
2you 2you pH reducer granules, 500 g

Alternative

2you 2you pH reducer granules, 500 g
5.0/10about £5.97
View offer
On this page
  1. 1.Start from the test, not the tub
  2. 2.Match the kilograms to the vessel
  3. 3.Read the listing before the price per kilo
  4. 4.Sodium bisulphate on the label

Start from the test, not the tub

pH minus is a reducer. You buy it when the water is too alkaline, not when the reading is already low. BISHTA's domestic hot-tub band is 7.0–7.6, and a reducer is the tool only when the fresh test is above 7.6. A low reading needs pH plus. Pool trade labels more often print 7.2–7.6, so the vessel still decides which label you follow. The powder is not a sanitiser and does not stand in for chlorine or bromine. A paddling pool that tested high is a reducer job. The same pool that tested low after heavy rain is not.

Match the kilograms to the vessel

Size follows litres, not the cheapest kilogram. A domestic hot tub here is often a few hundred litres up to about 1,500 litres, so a 500 g or 1.5 kg tub matches that volume. A 5 kg tub is the sensible buy for a season of corrections on a small garden pool. In this amazon.co.uk set the reviewed 5 kg price to beat is £18.25. Under £10 you will see the 2you 500 g at £5.97 and a £9.99 twin that is only half reducer. An 18 kg Bayrol bucket at £68.30 is the wrong object for a Lay-Z-Spa, because you then store a corrosive powder dry, away from chlorine and children.
Zagosa Zagosa pH minus granules, 1.5 kg

Testsieger

Zagosa Zagosa pH minus granules, 1.5 kg
6.2/10about £10.95
View offer

Read the listing before the price per kilo

A price per kilogram is only as good as the weight on the listing. Zagosa's 5 kg unit count is 5,000 g, and one bullet still says 1 kg. The 1.5 kg title says 1.5 kg, while the item type name says 1 kg. You do not know which line the warehouse followed. Shatchi is the clearer failure: a pack of two, a 2,000 g unit count, a 3 kg item weight and a 1.5 kg include line, at £18.60. The 2you set at £9.99 is 500 g of pH minus and 500 g of pH plus. Relax's catalogue field says Gel, while a UK review describes dissolving a dose. Do not reclassify that field yourself.

Sodium bisulphate on the label

Where a listing in this set names the chemical, it names sodium bisulphate, the dry acid PWTAG describes. That powder lowers pH, pulls total alkalinity down, and leaves sulphate in the water. The two pure 2you reducers print the name and a seller dose of 10 g per 1,000 litres for a 0.2 drop. Zagosa, Deep Blue, HTH, Bayrol, Waterman and Shatchi do not name it in the saved fields. A silent tub can still be the same chemical. You just cannot dose it from the product page. If the parcel has no gram table, use the label in the box. Dosing steps are on how to use pH minus.

Common questions

Is 500 g enough for a hot tub?
Often, for a domestic spa of a few hundred to about 1,500 litres, if you are correcting a modest high reading rather than fighting very high alkalinity all summer. The 2you 500 g tub is £5.97 and names sodium bisulphate. It has no review line, so the size can be right while the evidence is still thin. A 1.5 kg tub is the step up when you expect repeat doses. A 5 kg bucket is a pool-season object, not the default spa buy.
Who should not buy an 18 kg bucket?
A hot-tub owner, a paddling-pool owner, and anyone without a dry store away from chlorine products and children. Bayrol's 18 kg listing is £68.30. The price per kilogram looks low only if you will use the powder and can store it. A 500 g or 1.5 kg tub is the matching object for a spa.
What if the title and the unit count disagree?
Treat the listing as unfinished and do not calculate a price per kilogram from it. Shatchi's title, unit count, item weight and include line give four different fills at £18.60. Zagosa's 5 kg page still contains a 1 kg bullet. You can buy a different tub whose title, unit count and item weight agree, or you can wait for the seller to correct the page. Guessing which figure the parcel will follow is not a buying method.
Is a pH plus and pH minus twin pack the same as pH minus?
No. The 2you set at £9.99 is 500 g of increaser and 500 g of reducer. Buy it when your tests swing both ways and you want a small tub of each. Do not buy it as a pure reducer, because half the pack pushes pH up. The chemical on the minus half is not named on that listing, and there is no gram dose in the saved fields.
Should I compare price per kilogram across a 1 kg spa tub and an 18 kg bucket?
Only after the fill weight is consistent and you will actually use the larger pack. A 500 g tub at £5.97 can be the right spend for a spa even when an 18 kg bucket looks cheaper per kilogram. Bayrol at £68.30 is storage and a pack-format dispute, not an automatic saving. The litres you treat still beat a spreadsheet of pennies per gram.

Related pages

Best pH minus

pH minus for a hot tub

PH minus

How to use pH minus granules on a UK pool or hot tub

Sodium bisulphate vs hydrochloric acid for UK pools

Sources

Public UK sources used for this page in October 2026. Shelf prices and star lines are the amazon.co.uk figures for these eleven listings.

  1. PWTAG: Choosing an acid pH correctant (retrieved 21 October 2026)
  2. PWTAG: Carbon dioxide for pH control (retrieved 21 October 2026)
  3. PWTAG: Sulphate attack TN3 (retrieved 21 October 2026)
  4. HSE: Swimming pools (retrieved 21 October 2026)
  5. HSE: Managing health and safety in swimming pools (HSG179) (retrieved 21 October 2026)
  6. BISHTA: Water treatment (retrieved 21 October 2026)
  7. BISHTA: Daily, weekly, monthly and annual hot tub checks (retrieved 21 October 2026)
  8. All Swim: Pool acid safety data sheet (retrieved 21 October 2026)