mrburns
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In recent years, electrolytically derived hypochlorous acid cleaners have become quite popular in the hydroponics world. Thanks to some handy exemptions from manufacturing and handling requirements in the US (as stated in 40 CFR § 180.940), these cleaners are easy to produce and distribute to hydroponic growers. Even though they're more diluted than the traditional sodium hypochlorite cleaners, they still do a great job cleaning hydroponic reservoirs. The only downside is they can be a bit pricier due to their increased dilution and production process.
But don't worry! In this article, we'll show you how to whip up a solution similar to those fancy commercial hypochlorous acid cleaners using budget-friendly and easy-to-find products. The cool thing is that the resulting solution is pretty much the same as electrochemically derived hypochlorous acid. This is because the hypochlorite ion becomes protonated at low pH, which creates the desired substance during the preparation process.
Heads up: Hypochlorous acid can be unstable in highly concentrated solutions. If you bump up the concentration of the formulation too much, you might end up with a potentially dangerous release of chlorine gas when the pH is lowered. So, make sure to work in a well-ventilated area and stick to the recommended concentration amounts in this preparation. And as always, safety first! Be sure to read all the Material Safety Data Sheets (MSDS) of the substances used and wear appropriate personal protection equipment.
For the preparation, you will need the following items:
- Fresh Clorox (7.4%), no older than one week
- A 20 mL syringe
- Monopotassium Phosphate (MKP)
- Sodium Chloride (table salt is fine)
- Magnesium Sulfate
- Sodium Tripolyphosphate
- A calibrated pH meter
- A scale to weigh salts (±0.1g)
- A scale to weigh water (±0.1kg)
- Distilled or RO water (tap water is not suitable); distilled is preferable
- A clean, airtight, opaque plastic container (at least 1 gallon) for storing the resulting solution
Follow these steps to prepare the hypochlorous acid solution (values for approximately 1.2 gallons; can be scaled up for larger amounts):
- Calibrate your pH meter using fresh pH 4 and pH 7 buffer solutions.
- Fill the container with 3.6 kg of distilled water, referred to as the solution.
- Weigh and add 0.5g of Sodium Chloride to the solution, then stir until fully mixed.
- Weigh and add 0.1g of Sodium Tripolyphosphate to the solution, then stir until fully mixed.
- Measure 11mL of Clorox and add it to the solution. Adjust the amount accordingly if using a bleach solution with a different concentration.
- Stir until fully mixed.
- Weigh 0.5g of Monopotassium Phosphate and add it to the solution, then stir until fully mixed.
- Measure the pH of the mix. If the pH is >7, slowly add and fully mix small portions (~0.1g) of Monopotassium Phosphate until the pH is in the 6.5-7 range. Wait at least 1 minute between additions to ensure pH stabilization before adding more.
- Weigh and add 3.5g of Magnesium Sulfate to the solution, then stir until fully mixed.
- Add 0.9kg of water.
- Confirm the final pH is in the 6-7 range, and adjust with more Monopotassium Phosphate if needed.
This solution should offer medium-term stability and an active chlorine concentration comparable to products like Athena Cleanse. The anticipated hypochlorous acid concentration is approximately 0.02% (200ppm). Usage ranges from 2 to 10mL/gal of hydroponic nutrient solution, depending on the issue's severity. For general maintenance and minor infection treatment, 5mL/gal dosages should suffice.
Magnesium Sulfate and Sodium Chloride serve as stabilizers, while Mono Potassium Phosphate acts as a pH buffer and Sodium Tripolyphosphate functions as a cleaning agent to maintain clean irrigation lines (this can be excluded if not needed). Note that the mineral ions' contributions to the formulation's nutrition are minimal at the applied concentrations.
