Isothiazolone Biocide (CMIT/MIT) Storage & Tank Compatibility

Storing Isothiazolone Biocide (CMIT/MIT)? Start Here

Isothiazolone biocide (CMIT/MIT) is a broad-spectrum industrial microbicide built around two active isothiazolinones — 5-chloro-2-methyl-4-isothiazolin-3-one (CMIT) and 2-methyl-4-isothiazolin-3-one (MIT), commonly blended near a 3:1 ratio. Because the actives are chemically delicate, they are supplied as a stabilized aqueous concentrate (typically about 14% active) containing magnesium nitrate and magnesium chloride salts in water to prevent decomposition in storage and transit. The product controls bacteria, fungi, yeast, and algae and is dosed into cooling water, process water, fuel-system bottoms-water, paints and coatings, slurries, and metalworking fluids. Material of construction matters because the carrier is acidic and chloride-bearing: it corrodes common metals, and any iron, zinc, or copper that dissolves into the solution chemically deactivates the active ingredient — degrading both the equipment and the product at the same time. Choosing inert plastics protects performance and asset life.

Polyethylene (HDPE / XLPE) Compatibility

Polyethylene is compatible with stabilized aqueous CMIT/MIT biocide and is in fact the preferred storage and dosing material. The product is a water-based concentrate, and HDPE/XLPE resist its acidic, salt-laden carrier without corroding or leaching. Just as important for biocide efficacy, polyethylene is inert — it does not introduce the iron, zinc, copper, or aluminum ions that deactivate isothiazolinones, so the active stays potent throughout storage. A standard HDPE or crosslinked-polyethylene tank rated for the product’s specific gravity (roughly 1.2 for a 14% concentrate) is appropriate. Pair the tank with PP, PVC/CPVC, PTFE, or PVDF wetted hardware and FKM (Viton) elastomers; avoid metal valves, fittings, and pumps in the wetted path, and avoid natural rubber and EPDM seals. Keep the product cool, sealed, and out of direct light to preserve shelf life. Always confirm the rating against your specific product SDS and concentration.

Material compatibility at a glance

A stabilized aqueous CMIT/MIT biocide is water-based and metal-aggressive rather than plastic-aggressive: the acidic, chloride/nitrate-bearing carrier corrodes mild steel, zinc, copper, and aluminum, and dissolved metal ions deactivate the active. Polyethylene (HDPE/XLPE) is the preferred tank material because it neither corrodes nor contaminates the product. Use FKM (Viton) or PTFE seals and avoid natural rubber and EPDM.

Ratings: S suitable · C conditional / limited · U unsuitable. Verify against the cited resistance charts and your concentration/temperature before specifying.

The safety that actually matters

• Corrosive (H314): Causes severe skin burns and eye damage — wear chemical-resistant gloves, goggles, and face protection; have eyewash and safety shower available.
• Skin sensitizer (H317): Isothiazolinones are strong allergens (classified GHS Category 1A); repeated or even brief skin contact can induce allergic dermatitis — prevent all skin contact.
• Aquatic toxicity (H400/H410): Very toxic to aquatic life with long-lasting effects — provide secondary containment and never discharge to drains, soil, or surface water.
• Inhalation: Do not breathe mist, vapor, or spray; use local exhaust ventilation when handling or transferring.
• Incompatibilities: Keep away from strong oxidizers, strong bases (pH > 9 hydrolyzes the actives), and reactive metals; do not store in or contact copper, zinc, aluminum, or bare steel.
• Storage: Store sealed in HDPE/poly containers in a cool, dark, well-ventilated area within manufacturer temperature limits; provide spill containment.

Common questions

Can I store CMIT/MIT biocide in a polyethylene (HDPE or XLPE) tank?

Yes. Stabilized aqueous CMIT/MIT concentrate is water-based, and HDPE/XLPE is the preferred storage material — it resists the acidic carrier and, being inert, will not contaminate the product with metal ions. Choose a tank rated for the product’s specific gravity (about 1.2 for a 14% concentrate) and confirm against your SDS.

Why can't I use steel, copper, or aluminum tanks for this biocide?

The carrier is acidic and contains chloride and nitrate salts that corrode mild steel, galvanized/zinc, aluminum, and copper alloys. Beyond the corrosion, dissolved iron, zinc, and copper ions chemically deactivate the isothiazolinone actives, so a metal tank degrades both the equipment and the biocide’s performance.

What seals and fittings should I use?

Use FKM (Viton) or PTFE for seals, diaphragms, and seats, and PP, PVC/CPVC, PTFE, or PVDF for valves and dosing lines. Avoid natural rubber and EPDM, which degrade in this service, and avoid metal wetted parts that can corrode or deactivate the active.

Is CMIT/MIT biocide flammable?

No. As a stabilized aqueous concentrate it is water-based and non-flammable, which is why a representative NFPA/HMIS flammability rating is 0. The dominant hazards are its corrosivity (severe skin/eye burns), its strong skin-sensitization potential, and its high aquatic toxicity — not fire.