By The Zagosa Team. Published .
Reviewed or updated .
For the weekly once-over on a home hot tub, a decent set of test strips is fine. They only really let you down in three spots: low residuals, high cyanuric acid, and chasing down a problem. In those cases a photometer earns back its 70-pound price inside a single season.
What strips do well
Quick reads on free chlorine or bromine, pH, and total alkalinity. The colour patches are easy on the eye and you have a result in your hand within 30 seconds.
Weekly check-ups when you already know the water is roughly right. A strip will flag anything that has drifted far enough to need a look.
Calcium hardness in broad brackets. A strip can tell 100 from 250 from 500. What it struggles with is the 30-ppm precision that matters in the odd case.
Where strips let you down
Below 1 ppm free chlorine, strips often read zero whether the true level is 0.0 or 0.7. The colour shift simply is not linear down there.
Cyanuric acid strips are famously unreliable. Anything short of a turbidity test (the tube with the black dot at the base) is really just a guess.
On combined chlorine, strips are blind. You need a two-pad DPD strip or a drop test to see it.
When a photometer pays for itself
If you have ever burnt a week chasing a fault because the strip readings kept wandering, the photometer earns its keep. They give free, total, and combined chlorine to a decimal place, plus pH, alkalinity, and CYA, all in about 90 seconds.
A mid-range unit (Lovibond MD100, Palintest Compact, or similar) runs about 60 to 100 pounds for the meter, with reagents at a few pence per test.
For a tub used several times a week, or any commercial setting, that is the right level of kit.
Common questions
Are some strip brands genuinely better?
Yes. The cheap supermarket ones often have patchy print on the colour blocks. AquaChek and Lovibond are dependable for the money.
How long do strips keep once opened?
About six months from opening. Keep the cap tight and the bottle dry. A strip that has been splashed in the tub and dropped back in is a wasted strip and can spoil the rest.