Strips are quick and cheap but coarse. Photometers cost more and read precisely. Here is when each one is the right tool for a UK hot tub owner.
For routine weekly testing of a domestic hot tub, decent test strips are good enough. Where strips fall short is in three specific cases: low residuals, high cyanuric acid, and chasing a problem. For those, a photometer earns its 70-pound price tag inside a season.
Quick reads of free chlorine or bromine, pH, and total alkalinity. The colour patches are easy to read and the result is in your hand in 30 seconds.
Weekly check-ups when you know the water is roughly where it should be. Strips will tell you if something has moved badly enough to need attention.
Calcium hardness, in broad bands. Strips can tell you 100, 250, or 500. They struggle with the 30-ppm precision that matters in some cases.
Below 1 ppm of free chlorine, strips often read zero whether the actual level is 0.0 or 0.7. The colour change is not linear at the low end.
Cyanuric acid strips are notoriously inaccurate. Anything other than a turbidity test (like the test tube with the black dot at the bottom) gives you a guess.
For combined chlorine, strips are blind. You need either a two-pad DPD strip or a drop test.
If you have ever spent a week chasing a problem because the strip readings were inconsistent, the photometer pays for itself. They give you free, total, and combined chlorine to one decimal place, plus pH, alkalinity, and CYA, all in about 90 seconds.
A mid-range photometer (Lovibond MD100, Palintest Compact, or similar) is around 60 to 100 pounds for the unit and a few pence per test for the reagents.
For a hot tub used several times a week or for any commercial setting, this is the right level of kit.
Yes. The cheap supermarket ones often have inconsistent print on the colour blocks. AquaChek and Lovibond are reliable for the price.
Six months from opening. The cap must be tight and the bottle must stay dry. A strip that has been splashed in the tub and put back is a wasted strip and may contaminate the others.