Potassium Permanganate Storage — KMnO4 Fe/Mn Oxidation Tank Selection

Storing Potassium Permanganate? Start Here

The short version: the dilute purple solution you actually feed — usually a 2–4% mix for water treatment — stores just fine in a polyethylene tank. It will stain everything purple, but that’s cosmetic, not damage. The dry crystals are the part to respect: they’re a strong oxidizer and can start a fire if they touch fuel, oil, or other organics, so they get stored separately. Below: the tank to buy, the staining everyone asks about, the safety rules that actually matter, and what changes if it’s for drinking water.

Can you store it in a poly tank? Yes.

At the 2–4% strength used for water treatment, potassium permanganate is compatible with every common tank material — and polyethylene is the practical, affordable choice that most systems use. A standard HDPE or crosslinked (XLPE) poly tank handles the feed solution without trouble. Stainless steel is sometimes chosen for bulk day tanks only because the purple stain shows less on it — not because poly can’t do the job.

S = Suitable. Ratings from the Snyder Industries and Enduraplas published resistance charts (linked in Sources below).

Bottom line: buy an HDPE or XLPE tank rated for chemical service and you’re set. The only thing to plan around is the staining.

The purple staining — normal, not a problem

Everything the solution touches turns purple: tank walls, fittings, hoses, valve handles, your gloves. It’s permanent, and it’s completely normal — a thin cosmetic film of manganese, not a sign the tank or piping is failing. Fresh stains wipe off with a little sodium bisulfite or oxalic acid; set-in stains stay. Just expect it, budget gloves as a consumable, and don’t let it alarm you or your operators.

The safety that actually matters

Two rules cover almost everything:

• Keep the dry crystals away from anything burnable. The solid is a strong oxidizer. Store it well clear — 20+ feet, or behind a non-combustible barrier — from fuel, oil, glycol/antifreeze, pool chemicals, acids, and rags. In direct contact with those it can actually ignite. (The dilute solution doesn’t carry that fire risk.)
• Use the right seals. Viton (FKM) or PTFE gaskets and seats. Avoid Buna-N and natural rubber — they break down in contact with it.

Put the tank in a spill basin sized to 110% of the tank, keep that containment area clear of pallets/fuel/rags, and you’ve handled the essentials. A plain atmospheric vent (with a rain cap) is all the dilute solution needs — no scrubber.

If it’s for drinking water

Dosing potassium permanganate to pull iron, manganese, or taste-and-odor compounds out of drinking water? Use NSF/ANSI 60 certified product, and an NSF/ANSI 61 certified tank where the solution can reach finished water.

One tip from the field: start your dose low. Overdose leaves unreacted permanganate that turns tap water pink — and the customer calls start within hours. A quick jar test to set the dose avoids the whole headache. (For sizing: figure roughly 1 mg of permanganate per mg of iron, about 2 mg per mg of manganese, then confirm with a jar test.)

Common questions

Why does my feed line stain purple permanently?

It’s normal. A trace of the permanganate reduces to manganese dioxide and leaves a film on every wetted surface — poly, PVC, stainless, all of it. It’s cosmetic and doesn’t mean the pipe is degrading. Sodium bisulfite or oxalic acid removes fresh stain; set stain is permanent.

Can I store the crystals next to my pool chemicals?

No. The dry crystals are a strong oxidizer and need to be kept away from acids, fuels, glycols, and organics. Pool rooms usually have muriatic acid, algaecides, and sometimes fuel — any of those in contact with permanganate is a fire or toxic-gas risk. Give it its own segregated, dry spot.

Is it a substitute for chlorine?

For knocking out iron, manganese, H₂S, and some taste/odor — yes, it often beats chlorine. For disinfection — no. Most systems still chlorinate downstream for a disinfection residual. Think of them as teammates, not substitutes.

What tank size should I get?

Size the day tank for about 3–7 days of dosing and mix fresh weekly to keep the solution at full strength. A specific-gravity rating of 1.5 is plenty for the solution; the 1.9 SG chemical-service tanks we stock give you extra margin.