Reef Test Kit Mistakes That Give Wrong Readings

The mistakes that matter most

Bulk Reef Supply lists ten common testing mistakes. These are the ones that most often send reef keepers chasing problems that aren’t there.

• Expired reagents. They may not react properly. Check the date before every test, and write the opening date on the box.
• Not following the method. Too little sample, a sample taken next to a dosing line, reagent not fully dissolved, or reading the colour too late.
• Testing at different times. Alkalinity and pH shift through the day. Test at the same time each run.
• Uncalibrated meters. pH probes and salinity meters drift. Calibrate them regularly.
• Misreading colours. Colour charts are subjective and depend on light. Read them in the same light every time.
• Overcorrecting from one test. Confirm a surprising result before acting, then correct gradually.

Digital checkers have their own pitfalls

Hanna lists best practices for its marine Checkers. Wipe fingerprints off the cuvette, because they block the light path. Tap out air bubbles. Rinse with RODI water, not tank water, and let it dry fully. Don’t leave the reacted sample sitting in the cuvette, because it can stain the glass. Put the cuvette in the same way round every time.

A checker gives a precise-looking number, but it’s only as good as the sample and the cuvette.

Cross-check before you act

Every kit has a margin of error, and some suit certain ranges better than others. When a reading surprises you, test again. If it still looks wrong, compare with a second kit, a reference solution, or a reading from your local fish shop.

An ICP test can be a useful periodic check on your home kits, though it’s a snapshot from one day.

Write down how you tested

Note the kit, the time and anything unusual with every reading: a new box of reagent, a test straight after a water change, a meter just calibrated. When a reading jumps, those notes tell you whether the tank changed or the test did.

The Companion has a note field on every test for exactly this.

How long do reef test kits last?

Check the expiry date on the box and the maker’s guidance. Many reagents degrade faster once opened, especially in warm, damp places.

Why do two kits give different readings?

Different methods and margins of error. Pick one as your reference and use the other to cross-check.

Should I trust a fish shop test?

It’s a useful cross-check. Ask which kit they use.