Why We Use Plain Bleach in Our Reservoirs

We add regular unscented bleach (6–8.25% sodium hypochlorite) at 0.2 mL per US gallon of finished feed every time we mix a reservoir, and again every 4 days until we change the reservoir, dosed on the volume left: a 100-gallon reservoir takes 20 mL; with 50 gallons left, 10 mL. Stock concentrates get 1 mL per gallon of concentrate, in each container separately, and never in a tank that has RunClean in it: concentrated bleach and RunClean can release chlorine gas. When adding to a reservoir or injector line, the order is Part A → Part B → bleach → RunClean. It doesn't change pH, costs well under a dollar per 1,000 gallons, and adds about four times the available chlorine of the highest plant-fed HOCl rate we compared.

This is for the soluble program. Skip it if you're running beneficial microbes or Granular. There's no need to aerate tap water first.

Bleach and HOCl end up as the same chlorine

Bleach is sodium hypochlorite. It's commonly made by reacting chlorine with sodium hydroxide, which gives sodium hypochlorite, sodium chloride and water. A little excess sodium hydroxide keeps the bottle alkaline and stable in storage.

HOCl is hypochlorous acid. Commercial HOCl solutions are commonly made by electrolysis of salt water. For the comparisons below, we use each product's labeled HOCl concentration and assume the rest is water. That's a calculation assumption, not a claim about an undisclosed formula.

Once diluted, the split between hypochlorous acid and hypochlorite depends on the solution's pH. At a growing pH of 5.8–6.2, most free chlorine is in the HOCl form whether it went in as bleach or as an HOCl product. A bottle labeled HOCl doesn't give you a different form of chlorine in the reservoir.

What 0.2 mL per gallon adds

Our calculations use a regular unscented bottle at 7.5% sodium hypochlorite, in the middle of the 6–8.25% range. At that strength, 0.2 mL per gallon adds about 4.36 ppm sodium hypochlorite, or 4.15 ppm available chlorine before it reacts (using a density of 1.10 g/mL). Check the strength on your bottle; different strengths don't deliver the same amount at the same volume.

For the other ingredients, here is a manufacturer-disclosed plain bleach formula: 5.25% sodium hypochlorite, 4.12% sodium chloride and 0.1–0.2% sodium hydroxide, density 1.08 g/mL. It's a representative formula at a lower strength than regular bleach today, not the formula of every current Clorox bottle.

That's about 1.9 ppm total sodium. The sodium hydroxide reacts with the solution's acidity; it doesn't stay as free caustic in the reservoir. We haven't found this to be a harmful salt load at our rate. Scented, splashless and specialty cleaning bleaches are not substitutes.

Clorox's ingredient disclosure for the 121-fluid-ounce Regular bottle also lists sodium chlorate, poly(diallyldimethylammonium chloride), sodium-bisulfite-terminated polyacrylic acid and sodium carbonate, but not their percentages. So the table explains a disclosed plain-bleach formula; it isn't an exact analysis of that bottle, and the final ppm of those inactive ingredients can't be calculated from their names.

Dose and cost comparison

This compares one application to 1,000 US gallons of solution fed to plants, using one-gallon HOCl containers and a 121-fluid-ounce Clorox bottle. Products 1 and 3 use published MSRPs of $70 and $38 per gallon. Product 2 uses a $54 per gallon retail listing because we couldn't verify its MSRP. Clorox uses an $8.49 retail reference, also without a verified MSRP. Prices checked October 25, 2026; tax and shipping excluded.

All three HOCl products list 0.028% HOCl. We assumed a density of 1.00 g/mL for them and 1.10 g/mL for the 7.5% bleach. The active-ingredient column is the mass of the named chemical added; the available-chlorine column puts their oxidizing capacity on the same basis. These are calculated additions before reaction, not measured residual chlorine or predicted ORP.

• Product 1: 2–5 mL/gallon for maintenance, 5–10 mL/gallon for severe reservoir or media conditions, and 10 mL/gallon with RO water for the final plant-fed flush in its Blended feed chart. We include the flush rate for a full comparison; our finish still uses Cake.
• Product 2: 2 mL/gallon, daily or once weekly in weeks 1–6 on the label; its fluid feed schedules use it once weekly and only in certain weeks. That rate doesn't describe daily use for the whole crop.
• Product 3: 3–9 mL/gallon overall. Its standard mineral-feed program uses 3 mL/gallon; higher-EC feeds or added organics call for 5–9 mL/gallon because they raise oxidant demand. Its finish-stage chart also allows 3–9 mL/gallon.

Costs are per application, not per week or per crop; how often you apply and how much you treat set the total. Even Product 1 at 10 mL/gallon adds about 1.00 ppm available chlorine, against about 4.15 ppm from 0.2 mL/gallon of 7.5% bleach. That's why we use plain bleach. The amount added doesn't by itself prove equal performance or tell you how much oxidizer will remain.

Shock treatment between crops

Our shock rate is 10 mL of bleach per US gallon of water in an empty irrigation system, plants disconnected. That's 50 times the plant-fed rate; a 100-gallon cleaning batch takes 1,000 mL. Flush the system with clean water before you reconnect plants. Same bottle strengths and prices as above, per 1,000 gallons of cleaning water:

The makers of Products 1 and 2 use separate cleaning products with different chemistry for system resets. Product 1's 5–10 mL/gallon severe-condition rate is a plant-fed rate and is in the chart above. Surface-spray rates are not line-shock rates.

These figures are chlorine added before reaction, not the residual after cleaning. Keep shock solution away from plants and foliar sprayers, and never mix it with acids, RunClean, ammonia or another cleaner. Bleach kills growth but leaves dead residue behind; we remove that separately with an enzyme. See removing dead organic matter after biofilm.

Why we add it again every 4 days

Chlorine gets used up as it reacts with material in the reservoir and irrigation system, and ORP usually falls as it does. The first dose doesn't protect the reservoir for its whole life, so we top it up every 4 days until we change the reservoir, at 0.2 mL per gallon of solution left.

A label can't tell you the millivolt increase. The same dose reads differently in clean water and in a nutrient reservoir with heavy oxidant demand, and more chlorine doesn't mean a proportionally higher ORP. Comparing products means testing them in the same finished feed. See how we use ORP.

Bleach in stock concentrates

Add 1 mL of plain bleach per gallon of concentrate, to each container separately. The 0.2 mL rate is for finished feed, not concentrate. If you already see floaters, add the bleach and strain them out through cheesecloth or a coffee filter; the concentrate is still fine to use. Store concentrates in dark or opaque containers and re-dose monthly if they sit. Never put bleach in a tank that has RunClean in it; concentrated bleach and RunClean can release chlorine gas. More in mixing stock tanks and concentrates.

When the contamination keeps coming back

In our experience, black aquarium pumps that biofilm has gotten into can't be sterilized and need to be replaced. We've seen the same with air stones. Replace them, clean the reservoir and the rest of the irrigation system, and start with fresh feed. Don't keep raising the dose to make up for contaminated equipment; a good ORP reading in the tank doesn't mean the inside of the pump is clean.

RunClean handles a different job: mineral scale and pH down. It doesn't replace the bleach. Keep concentrates separate and never mix concentrated bleach with RunClean, another acid or ammonia; bleach and RunClean concentrates can release chlorine gas.