Sodium hypochlorite looks like an easy storage problem. It is water-thin, it is not flammable, and polyethylene handles it well. The complications are the ones you cannot see.
It off-gasses, so venting is not optional
As hypochlorite decomposes it releases oxygen. In a sealed tank that gas has nowhere to go. Pressure builds slowly, and a polyethylene tank was never designed to hold pressure. It deforms, bulges near the top, or splits at a fitting.
The failure we actually get called about is simpler. A vent packs solid with salt crystals or a screen clogs, nobody checks it, and the next fill pushes the tank past what it can take.
Three rules keep this boring:
- Size the vent for the fill rate, not just for off-gassing. The fastest air movement happens while product is being pumped in.
- Keep the vent clear of the fill path so splash cannot dry and crust inside it.
- Put vent inspection on a written schedule. Quarterly is reasonable.
Heat and sunlight cost you product
Hypochlorite decomposes faster when it is warm, and faster still in sunlight. A translucent tank sitting in Texas sun is a slow bleach destroyer. Available chlorine drops, the operator compensates by dosing more, and that shows up on the chemical bill every month.
Use an opaque tank. Black or dark green blocks light. If the tank lives outdoors, shade helps, and so does keeping it off a west-facing wall that bakes all afternoon.
It is heavier than water
A 12.5% solution runs around 1.2 specific gravity. That sits comfortably inside a standard 1.5 rated tank, but it is not water. Use the real number when you size a stand, a slab, or a containment basin.
Hardware and metals
Hypochlorite attacks many metals, including stainless grades over time. Wetted hardware should be a compatible plastic. Titanium works where metal is unavoidable. Do not let a stainless nipple end up in a bleach tank because it happened to be on the truck that day.
Bottom line
Vent it properly, keep light off it, use compatible hardware, and actually inspect the vent. Bleach tanks that follow those four rules run for years. The ones that fail early almost always fail for the same reason, and it is the vent nobody looked at.
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