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Salinity meter buying guide

Updated: 22 October 2026

You are choosing a salinity meter for a reef, a fish-only marine tank, or a salt chlorinator, and amazon.co.uk is offering three different instruments under one name. A £14 refractometer, a £30 pen and a £116 monitor do not answer the same question. This salinity meter buying guide is the decision that sits in front of the [salinity meter comparison](/hub/measuring-equipment/salinity-meter): which tool, and which unit, matches the water you already keep. The twelve listings were priced on amazon.co.uk on 21 October 2026. Products Compared did not run a lab test. A qualifying purchase can earn us a commission at no extra cost to you.

You are choosing a salinity meter for a reef, a fish-only marine tank, or a salt chlorinator, and amazon.co.uk is offering three different instruments under one name.

Our top picks

Agriculture Solutions Agriculture Solutions WL0020-ATC

Best overall

Agriculture Solutions Agriculture Solutions WL0020-ATC
9.0/10about £13.99
View offer
UIUZMAR UIUZMAR UI-09A pen

Alternative

UIUZMAR UIUZMAR UI-09A pen
7.6/10about £29.99
View offer
XRCLIF XRCLIF refractometer

Best value

XRCLIF XRCLIF refractometer
8.1/10about £13.99
View offer
On this page
  1. 1.Three tools share the name
  2. 2.ppt, ppm, and specific gravity
  3. 3.What the cheap wide-range refractometers do not claim
  4. 4.What to check on the listing

Three tools share the name

An optical refractometer in this set takes two or three drops, bends light through a prism, and shows a scale. It does not give you pH. The optical rows run from £13.99 to £17.85, and the titles advertise about 0–100 ppt. None says natural seawater or PSU. A digital pen infers salt from conductivity and usually adds pH, TDS, EC and temperature. Pens here sit at £27.99 to £36.99, with one 9-in-1 at £54.90. Several print a pool band of 2700–3400 ppm. That band is a listing bullet, not every UK chlorinator. A Wi-Fi monitor is a third type, and the unit still comes before the brand.

ppt, ppm, and specific gravity

Reef water is usually talked about near 35 ppt. Camlab states that 35 ppt is the same as 35,000 ppm, or 3.5 percent. Hayward UK says a typical AquaRite cell wants about 3–4 g/L, with low-salt systems nearer 1.5 g/L, and that the manual comes first. A pool at 3,200 ppm is 3.2 ppt. A reef at 35 ppt is about ten times saltier. If your meter shows 3 and the chlorinator manual says 3000, you may be looking at ppt when the manual means ppm. If the meter cannot show the unit your livestock or your cell already uses, it is the wrong meter. Targets stay on the aquarium and pool guide.
Agriculture Solutions Agriculture Solutions WL0020-ATC

Testsieger

Agriculture Solutions Agriculture Solutions WL0020-ATC
9.0/10about £13.99
View offer

What the cheap wide-range refractometers do not claim

D-D, writing for Practical Fishkeeping readers, says many hobby refractometers are scaled for brine, and that 35 ppt seawater can read about 36.5 ppt on a brine scale. These amazon.co.uk titles do not say they are brine-scaled or seawater-scaled. They say 0–100 ppt, so do not add 1.5 ppt to every row. A £14 meter can still be the first tool if you will zero it and keep one method. It is a poor substitute when corals depend on a scale that already means natural seawater. Specialist meters sit outside this set, from about £35 for a D-D or TMC refractometer to £108.36 including VAT for Hanna's HI-98319. Those shop prices are not a test of this set. ATC is a claimed window, not permission to ignore temperature. XRCLIF prints 10–30 °C. BOWONG's bullets say both 0–10 °C and 10–30 °C, so you cannot quote one window. Prism and probe are compared on the refractometer and digital meter page.

What to check on the listing

Read the unit before the stars. Agriculture Solutions WL0020-ATC, titled Aqueous Lab, is 4.6 from 4,704 ratings at £13.99. That is coverage, not a laboratory rank. HXTDBY is 4.8 from 38 ratings, and one UK review could not zero below specific gravity 1.005. The 9-in-1 pen is 5.0 from four non-UK reviews. A refractometer you can zero needs a screwdriver, RO or deionised water, and a scale you can focus. XRCLIF and Agriculture Solutions both name a case, a dropper or pipette, a cloth and a screwdriver. YINMIK YK-5SEU claims six powder packs, and the file ASIN B0CN4NJZ89 is not the product URL B0C6P4V4FR. These hobby testers are outside the Measuring Instruments Regulations 2016 list. If the line will not focus, the Consumer Rights Act 2015 is the route back to the seller.

Common questions

Is a £14 refractometer enough?
It can be enough for mixing marine salt at home if you zero it and accept a wide 0–100 ppt scale. In this set that price is £13.99 to £17.85. It is not a seawater-calibrated instrument, and D-D's brine warning is about that class of meter. Move to a named seawater refractometer or a Hanna-class tester when the tank depends on a scale that already means natural seawater.
Will a 5-in-1 pen replace a refractometer on a reef?
Not on the evidence in this file. The pens add pH, which a prism does not, and UK reviews on UIUZMAR and YINMIK say a good pH reading did not mean the salinity matched a reef or a Hanna meter. Use a pen when ppm and pH are the job. Use a prism, or a purpose-built conductivity tester, when the number that matters is near 35 ppt.
Do I buy for ppt or for ppm?
Buy the unit your target already uses. Reef talk is ppt or specific gravity at a stated temperature. Salt cells are ppm or g/L, and the cell manual wins over a 2700–3400 ppm bullet. Camlab's conversion is 35 ppt equals 35,000 ppm, so the two numbers are not interchangeable on a screen that shows only one of them.
Does ATC mean I can ignore temperature?
No. ATC is a claimed window, and only some listings print one. XRCLIF states 10–30 °C. A UK review of the Agriculture Solutions meter still says to zero on fresh water at the same temperature as the sample. A hot sample against a cold zero is a common way to invent a salinity change.
Are these meters UKCA measuring instruments?
Do not shop for that mark. The Measuring Instruments Regulations 2016 do not list hobby salinity testers. You still have ordinary consumer rights if the goods are not as described, and the product still has to be safe. No British Standard is printed on these twelve listings.

Related pages

Best salinity meter

Salinity meter

Aquarium salinity meter vs pool salt tester targets

How to use a salinity refractometer: zero, then read

Refractometer vs digital salinity meter on your reef

Sources

Public UK sources from the research digest, last checked on 21 October 2026. Shelf prices and star lines are the amazon.co.uk figures captured with these twelve listings. The price bands are this set, not a market average.

  1. Hanna Instruments UK: HI-98319 salinity tester (retrieved 21 October 2026)
  2. Practical Fishkeeping: D-D seawater refractometer (retrieved 21 October 2026)
  3. D-D The Aquarium Solution: salinity and specific gravity (retrieved 21 October 2026)
  4. Hayward UK: salt concentration for salt chlorination (retrieved 21 October 2026)
  5. Camlab: measuring the salinity of seawater (retrieved 21 October 2026)
  6. HORIBA UK: aquarium water testing (retrieved 21 October 2026)
  7. Finest Aquatics: Tropic Marin high-precision hydrometer (retrieved 21 October 2026)
  8. GOV.UK: Measuring Instruments Regulations 2016 (retrieved 21 October 2026)