Evaporative cooling pad maintenance: scale, algae and when to replace

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Short answer: most pad problems come from the water, not the pad. Keep the water pH between 6 and 8, bleed off some water all the time so minerals do not build up, wet the whole pad evenly, and let the pads dry out fully once every 24 hours to hold back algae. Inspect monthly, drain and clean the whole system every quarter of the cooling season, and replace pads that sag, are clogged with scale, or are breaking down.

How a pad cools

Outside air is drawn through wet pad media. Water evaporates into the air and the air cools. How much it cools depends on the wet-bulb depression, the gap between the dry-bulb and wet-bulb temperature. Well-kept modern pads can reach 80% efficiency or more, and with a well-designed ventilation system they can lower incoming air temperature by about 5–15 °F (about 3–8 °C). In humid weather the possible drop is much smaller.

Water quality and bleed-off

• pH: aim for 6–8. If it is higher, acid treatment may be needed.
• Bleed-off: as water evaporates, salts and minerals stay behind and concentrate. Draining a small, steady flow and replacing it with fresh water keeps them diluted. Follow the pad maker's figure; a common starting point is about 1 US gallon per hour per foot of pad length for a 4 ft high, 6 in thick pad, adjusted for pad size and water hardness. Increase it for hard water and reduce it for soft water.
• Route the bleed water to a proper drain.

Without enough bleed-off, scale forms on the pad surface, evaporation drops, and air resistance rises — which also reduces fan output.

Wet the whole pad

Dry streaks mean lost cooling. A typical flow is about ¾ US gallon per minute per foot of pad. If you see dry sections, check the pump, the distribution pipe and its holes; scale or algae often plugs them.

Control algae

Algae raises the pad's air resistance and breaks down cellulose media. To control it:

• Let the pads dry fully once every 24 hours — for example, set the controller so the pads only run above the night-time temperature, or use a timer to stop them for a few hours early in the morning.
• Keep direct sunlight off the pads and the sump where possible.
• Keep leaves, dust, insects and grass clippings out of the sump — they feed algae.
• Use only chemicals the pad maker approves. Do not add chlorine bleach or bromine; they shorten pad life. Quaternary-ammonium products are commonly recommended for continuous algae control, and cleaning products with an organic acid help remove scale.

Maintenance checklist

Monthly during the cooling season

• Look for scale; if present, increase bleed-off.
• Look for algae; if present, increase daily dry time and review water treatment.
• Clean filters.
• Walk the pad wall: sagging, holes, bird nests, dry sections.

Quarterly (start of season, mid-season, shut-down)

• Drain and disinfect the whole system.
• Clean distribution pipes and the top assembly.
• Remove solids from the sump and gutters.
• The start-of-season clean matters most if pads stay installed all year.

When to replace pads

Replace pads when cleaning no longer restores them: media that sags or collapses, surfaces crusted with scale, soft or crumbling cellulose, or holes and damaged edges that let air bypass the pad. Replacing a section with the same flute code and thickness keeps air resistance even along the wall.

Replacement pads from EcoHarvest

EcoHarvest supplies cellulose pads in flute codes 5090, 6090, 7090 and 7060, in 100 mm, 150 mm and 200 mm thickness, plus flame-retardant cellulose where it is required. See cooling pads. Saturation, pressure drop and fire rating (where applicable) are confirmed on the written quotation.

For a replacement quote, send: pad wall length and height, current flute code and thickness, cellulose or flame-retardant, water quality notes if known, and country.

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