Most skylight cleaning robots want a neutral detergent at 0.5-1.5 percent dilution by volume in 2026. Above 2 percent you risk streaking and, on coated glass, permanent haze. Use deionised water for the final rinse if the site has hard water.
Operators often treat the detergent tank like a soap dispenser and eyeball the pour. That works on a garden hose. On a robot with a 12-litre tank and a metering pump, guessing costs money twice: once in wasted chemical, once in callback cleans to fix the streaks.
How much detergent should you dose?
Start at 0.5 percent for routine dust removal on interior atrium glass. Move to 1 percent where the roof collects traffic film or pollen. 1.5 percent is the ceiling for exterior glazing with visible bird soil, and only as a spot pre-soak, not a full-cycle dose. A Lingfeng S1’s pump doses in millilitres per minute, so check the calibration once a month; drift of 20 percent is common after 500 hours.
Why pH matters more than foam
Foam looks impressive and cleans nothing extra. What lifts baked-on mineral film is the right pH. Neutral (pH 6-8) is safe for every common glass coating and for the anodised aluminium frames most skylight robots grip. Alkaline cleaners above pH 10 strip some hydrophobic coatings in a single season. Acidic descalers below pH 3 will attack the frame seals. Neither belongs in a routine robot programme. If you have hard-water spotting, treat it as a separate maintenance task, not a stronger daily mix.
What water quality does a skylight robot need?
Total dissolved solids matter as much as the detergent. Feed water above 200 ppm TDS leaves spots as it dries in the sun, no matter how good the chemical is. In Shanghai or coastal sites, run the fill through a 5-micron sediment filter and, ideally, a resin deioniser. The Lingkong K3 handles either, but the rinse result on a bright skylight above a retail floor is where customers judge you.
| Glass condition | Dose (% vol) | pH target |
|---|---|---|
| Interior dust only | 0.5 | 7 |
| Exterior traffic / pollen | 1.0 | 7 |
| Bird soil (spot) | 1.5 | 8 |
| Hard-water scale | separate task | acid, manual |
Who should skip chemicals entirely
Sites with new low-E or self-cleaning glass should run plain deionised water for the first 12 months. The coating needs to cure. Adding chemicals early, even neutral ones, risks a warranty argument you will lose. Same for museum skylights where residue near artefacts is a conservation issue; there, dry microfibre plus filtered water is the only defensible method.
The risk nobody budgets for
Chemical overspray on a sloped roof runs downhill. On a 25-degree skylight over planters or a car park, that runoff stains stone and damages paint. Fit a drip tray under the parked robot and never leave a fully dosed tank overnight. If your site has a water treatment or grease trap, confirm the detergent is biodegradable to keep the discharge permit clean. We cover the compliance side in our safety and compliance guide.
Key Takeaways
- Dose neutral detergent at 0.5-1.5 percent; never above 2 percent routinely.
- Match pH to the glass coating, not to foam volume.
- Keep feed water under 200 ppm TDS or you will get sun-dried spots.
- New low-E and self-cleaning glass: water only for the first year.
- Manage sloped runoff and tank storage to avoid staining below the roof.