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Aquarium salinity meter vs pool salt tester

Updated: 22 October 2026

You keep a reef, or you are about to, and the same cupboard has to cope with a salt chlorinator. The aquarium salinity meter vs pool salt tester problem is that both hobbies say salt and then use numbers about ten times apart. A meter that is honest at 35 ppt can look broken at pool strength, and a pool pen at 3,200 ppm is not a failed reef. This page is about targets and units. Prices are the amazon.co.uk listings in the [salinity meter comparison](/hub/measuring-equipment/salinity-meter) on 21 October 2026. Products Compared did not run a lab. A qualifying purchase can earn a commission at no extra cost to you.

You keep a reef, or you are about to, and the same cupboard has to cope with a salt chlorinator.

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.The two targets
  2. 2.What the chlorinator manual overrides
  3. 3.What a reef refractometer is bad at
  4. 4.Which listings match which job

The two targets

Camlab states that average seawater is 35 ppt, which is 35,000 ppm, or 3.5 percent. HORIBA UK pairs 35 ppt with specific gravity 1.025. Tropic Marin's UK retailer pairs 35‰ with 1.026 at 25 °C, with fish-only tanks often around 1.023–1.025 and reefs around 1.025–1.027 at that temperature. Quote the temperature. Do not collapse those sources into one official specific gravity. A salt cell is usually in the low thousands of ppm. Hayward UK says an AquaRite system is generally 3–4 g/L, and that low-salt versions are about 1.5 g/L. The manual comes first. One ppt is 1,000 ppm, so a pool at 3,200 ppm is 3.2 ppt. If your refractometer shows a number near 3 while the chlorinator wants 3000, you are looking at two units, not a dead cell. This page does not set a pond treatment dose.

What the chlorinator manual overrides

The 2700–3400 ppm line on UIUZMAR and YINMIK bullets is a sentence in those listings, paired with pH 7.2–7.8. It is not a UK legal salinity, and it is not every cell. Palintest says manufacturer ranges often fall between 1500 and 4500 mg/L, that you should test about weekly, and that low salt means weak chlorine while high salt can damage the cell. That does not replace your chlorinator manual. Hayward's low-salt figure of about 1.5 g/L is the example to keep. A listing that pushes you to 3,200 ppm will oversalt that system. If the manual and the bullet disagree, follow the manual. A pen that holds pH and wanders on salinity is useful for the pH half and useless as the only salt check.
Agriculture Solutions Agriculture Solutions WL0020-ATC

Testsieger

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

What a reef refractometer is bad at

The optical meters show about 0–100 ppt, with a division of about 1 ppt. At 35 ppt that step is a small slice. At 3 ppt it is a third of the target. You can see that the pool is salty. You cannot claim 3,200 ppm rather than 2,800 ppm from a 1 ppt line. A reef refractometer is the wrong tool if you only own a pool. UK reviews on UIUZMAR UI-09A and YINMIK YK-5SEU say the salinity channel was not close for a reef even when pH could be calibrated. Write the unit on every reading. Prism versus probe is on the refractometer versus digital page. Instrument types are in the buying guide.

Which listings match which job

For marine water, the optical rows talk about seawater, ppt and specific gravity. Agriculture Solutions WL0020-ATC at £13.99, titled Aqueous Lab, is 4.6 from 4,704 ratings and is the top pick for a budget marine mix if you zero it. XRCLIF at the same price states ATC at 10–30 °C. None of them resolves a few hundred ppm. For a salt pool, the 5-in-1 pens speak ppm and pH together. UIUZMAR UI-09A at £29.99 includes calibration powder. Both it and YINMIK YK-5SEU name 2700–3400 ppm in the bullets. Use that only if your manual agrees. Do not promote either pen to a reef salinity meter because the title says aquarium. The optical zero is on the how to use page. TEKCOPLUS at £115.99 has eight reviews. Price does not solve the unit problem. Use ppm for the cell and ppt for the reef.

Common questions

Why does my pool read about 3 ppt when the chlorinator wants 3000?
Because 3,000 ppm is 3 ppt. Camlab's seawater figure of 35 ppt is 35,000 ppm, so a pool at Hayward's typical 3–4 g/L is roughly a tenth of reef strength. Change the unit on the meter, or change the meter, rather than adding salt until a ppt scale looks like 3000.
Can one refractometer do the pool and the reef?
It can tell you the pool is far less salty than the reef, and it can run the reef if you accept a wide 0–100 ppt scale and a proper zero. It cannot resolve a few hundred ppm at pool strength when the division is 1 ppt. A ppm pen is the better pool tool. Do not expect that pen to be precise at 35 ppt unless you have checked it there.
Is 2700–3400 ppm the UK legal level?
No. It is a bullet on UIUZMAR and YINMIK listings, with pH 7.2–7.8. Hayward UK says generally 3–4 g/L, low-salt about 1.5 g/L, and the manual first. Palintest's published manufacturer span is often 1500–4500 mg/L. Your cell manual overrides all of those.
What salinity is a reef, in ppm, so I can compare?
About 35,000 ppm if you are using Camlab's statement that 35 ppt equals 35,000 ppm. A pool at 3,200 ppm is 3.2 ppt beside that. Specific gravity for the same reef water is 1.025 on HORIBA's page and 1.026 at 25 °C on Tropic Marin's UK retailer page. Do not average them.
Do koi salt baths use the pool number?
Not by any dose on this page. Reviews show koi keepers using these pens for pH and for a salt level they already planned. Follow that plan, or a fish-health source, rather than copying 2700–3400 ppm from a pool bullet or 35 ppt from a reef.

Related pages

Best salinity meter

Salinity meter

Salinity meter buying guide: choose ppt, ppm or a pen

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)