An HOCl Testing Toolkit: Paper, High-Range Strips and a Photometer

An HOCl testing toolkit is how you check what a batch actually is after the generator stops. The timer is not the measurement. You need a way to read concentration in parts per million (ppm) and a separate way to read pH. This page is about which papers, strips and meter to keep on hand, what comes free with an Eco One order, and when the 10–200 ppm paper is no longer enough. The method itself — dip times, the pH 5–6 target, and the Eco One manual’s 1:5 dilution — is in HOCl PPM and pH Basics.

HOCL LLC sells machines and the test supplies linked here. It does not sell bottled HOCl.

What comes with an Eco One order

HOCl test paper (10–200 ppm) and pH test paper come free with every Eco One order; refills are sold separately. Those two papers are the starting kit for a 1-liter home batch. Replacement HOCl test paper (10–200 ppm) is sold as a 15-foot (5-meter) roll with color matches at 10, 50, 100 and 200 ppm. Replacement pH test paper is a 15-foot roll with a color match at each full pH unit from 0 to 14.

Use chlorine paper for concentration and pH paper for pH. They are not interchangeable. Read each paper as its package directs: a short strip, the listed dip and wait, and a match to the printed chart in good light. Do not invent a number that is not on the chart.

For a Hypo 7.5 batch, follow that model’s manual, which calls for high-range chlorine strips and separate pH strips; the testing notes are on Choosing an HOCl Generator. The 1:5 method below is the Eco One manual’s method.

When to replace the paper

There is no separate published “replace every n months” figure for these papers. Treat the pack as the authority. Keep chlorine paper and pH paper dry, in their packaging, and away from heat and moisture. Use a fresh short strip for each reading; do not reuse a dipped strip. Replace a roll or pack when it is used up, when it is past any date printed on the pack, or when the color chart is faded, stained or hard to match. If a new batch that you made by the book gives a blank or badly off reading, check the paper’s condition before you assume the machine is the only variable.

When a batch is above the 10–200 ppm paper

The included chlorine paper covers the Eco One’s 40, 60, 100 and 200 ppm programs when the batch is near those targets. It does not, by itself, display 500 ppm. A 500 ppm Eco One liter — 2 g of kosher salt, 2 teaspoons of 5% distilled vinegar, and the 40-minute run in the how-to — is above that printed scale.

The Eco One manual’s method for a reading above 200 ppm is a 1:5 dilution: 1 part HOCl plus 4 parts water, then multiply the paper reading by 5. A short worked example: you mix 10 mL of the finished batch with 40 mL of distilled water; the paper reads 100 ppm on that diluted cup; 100 × 5 = 500 ppm in the original batch. Measure pH on the undiluted solution, not on the diluted cup. The full steps, including why distilled water matters, are in PPM and pH Basics. That 1:5 cup is only a way to read concentration. It is not a use direction.

High-range strips and a photometer

If you want a meter reading instead of a color match, for batches inside the meter’s listed range, the store also sells a photometer. Two facts from the current product pages matter before you buy:

• The eXact Micro 7+ photometer is used with high-range free-chlorine strips, which are sold separately. The store lists a free-chlorine range up to 250 ppm, a test that takes about 20 seconds, and no calibration step. It reads chlorine, not pH; keep pH paper for pH.
• The eXact high-range chlorine strips (a bottle of 50 tests) require that photometer. They are not a stand-alone color-match strip in the way the 10–200 ppm paper is.

Because the listed photometer range stops at 250 ppm, a 500 ppm batch is still above that range if you dip a full-strength sample. Do not treat the meter as a direct 500 ppm reader. For Eco One batches above 200 ppm, the method already in the manual is the 1:5 dilution with the 10–200 ppm paper. This page does not invent a second dilution protocol for the photometer; follow the meter’s own instructions for any sample it can read, and keep the 1:5 paper method for a 500 ppm Eco One liter unless a current manual says otherwise.

pH is a separate test

ppm and pH answer different questions. Concentration tells you how much free chlorine the paper or meter is reading. pH tells you whether the batch is in the 5–6 window that HOCL LLC’s Eco One and Hypo 7.5 directions aim for. A 200 ppm reading at the wrong pH is not the same batch as 200 ppm at pH 5–6.

Use pH paper on the undiluted batch. The pH paper roll (0–14, 15 feet) is the store’s pH paper for Eco One batches. If you prefer pre-cut strips, a pack of 80 pH strips is also sold; the store describes that pack as a color match at each full pH unit from 1 to 14. Either format is a pH test, not a chlorine test.

The pH 5–6 target, the short shelf life at pH 4–5, and the chlorine-gas warning below pH 4 are in the ppm-and-pH guide. If pH is high after a run, do not guess at a large extra vinegar addition; make a new batch with the vinegar amount in the manual.

Never mix HOCl solution with ammonia, bleach, strong acids or other cleaners; mixing with ammonia can release chloramine gas, and mixing with strong acids can release toxic chlorine gas. Add only the vinegar or additive your manual specifies, in the amount it specifies. If someone breathes in fumes or swallows solution, call Poison Help at 1-800-222-1222 (poisonhelp.hrsa.gov).

Stock the kit

A practical kit for Eco One users looks like this:

• The Eco One itself. HOCl test paper (10–200 ppm) and pH test paper come free with every Eco One order; refills are sold separately.
• Replacement 10–200 ppm HOCl test paper.
• Replacement pH paper, or the 80-pack of pH strips if you would rather not tear from a roll.
• Distilled water and a small, measured cup or two, if you will use the 1:5 method on 500 ppm batches.
• Optional, if you want meter readings within the range the store lists for the meter (up to 250 ppm): the photometer and a bottle of high-range strips. Buy them as a pair; the strips need the meter. For a 500 ppm Eco One liter, use the 1:5 method above.

You do not need the photometer to start. Most home 200 ppm liters are inside the 10–200 ppm paper’s chart.

Re-test after storage

A reading taken when the batch is fresh is not a reading for a jug that has been sitting. Heat and air degrade HOCl, light protection is part of the storage rule, and a finished pH of 4–5 means a very short shelf life. Re-test both ppm and pH after storage and before you rely on an older container. The conditions — closed, protected from light, at room temperature or cooler, in HDPE, LDPE or PET — and the Eco One manual’s storage statement are in HOCl Storage and Shelf Life.

Label the jug with the date, the ppm reading and the pH. If concentration has dropped below what you need, or pH has moved out of range, make a fresh liter rather than trying to “correct” the stored solution.

If you are still learning the recipes, How to Make Hypochlorous Acid at Home puts these checks at the end of a 200 or 500 ppm Eco One run. How an HOCl Generator Works explains what the machine is doing in the pitcher.

Keep the papers dry, replace them when they are worn out or past date, and do not ask one strip to do both jobs. To get started with a machine that comes with the first papers free, use the Eco One.