Use pH-neutral to mild alkaline cleaners (pH 7-10) with skylight robots. Acid below pH 4 etches glass, ammonia attacks frame seals, and abrasive powders scratch coated panes permanently.
Buyers focus on the machine and treat the fluid as an afterthought. Then a site uses a strong descaler to shift hard-water spots and the glass clouds over. Cleaning chemistry is where a cheap decision turns into an expensive one – and glass damage is not reversible.
What should you never put through a robot?
Three families are off limits. Acidic descalers and vinegar-based mixes below pH 4 attack the glass surface and any low-E coating. Ammonia and strong alkaline above pH 11 degrade the rubber seals and suction cups, shortening their life by months. Abrasive powders and pads scratch both glass and coating in a single pass.
- Never: vinegar, hydrochloric descalers, ammonia, scouring powder
- Careful: high-foam detergents clog filters and leave streaks
- Safe: pH-neutral surfactant, mild alkaline (pH 8-10) for oily film
- Safe: filtered water rinse at the end of every pass
Does chemistry affect the suction cups?
Yes, directly. Cups are the first part to fail on any robot, lasting 6-12 months in regular use. Aggressive alkalines harden the rubber and cut that to 4-6 months, which means a cup set every season. Mild solutions keep the rubber supple. If your cups feel stiff or glazed, look at the fluid before blaming the supplier.
Dilution matters as much as the product. A dose of 1:100 surfactant is plenty for routine dust. Doubling it does not clean faster; it leaves residue that attracts dust and shows as streaks in sunlight. The Lingfeng S1’s filtration loop works best with low-foam fluids, so keep the mix lean.
How do you handle hard-water spots?
Do not reach for acid. Address the source: filtered or softened rinse water. Scale spots form when rinse water above 200 ppm total hardness evaporates. Fix the water and the spots stop appearing. For existing scale, use a mild citric-free alkaline gel with dwell time and repeated wet passes rather than a strong acid.
| Problem | Wrong fix | Right fix |
|---|---|---|
| Hard-water spots | Acid descaler | Filtered rinse + alkaline gel |
| Oily film | High-foam soap | pH 8-10 low-foam cleaner |
| Bird droppings | Ammonia | Mild alkaline + dwell |
| Dust only | Strong detergent | Water with light surfactant |
Who should dilute more carefully?
Anyone with coated low-E glass, and sites near food or pharma where residue carries contamination risk. Those buildings should run the leanest mix and rinse with filtered water every time. Buildings with plain clear glass have more tolerance, but there is no upside to a heavier dose – only streaks and sticker cups.
Ask any supplier for the full chemical datasheet before buying. Check how the rinse loop handles residue with water filtration and hard-water control.
How do you test a new cleaner safely?
On a spare pane, not on the building. Buy or borrow a coated offcut matching your glazing and run three passes with the proposed mix. Check for coating haze, seal swelling and residue under a bright light. Ten minutes on a sample pane is the cheapest insurance against damaging a whole façade with the wrong fluid.
Then test on the least visible panel of the real roof before the whole run. Observe in daylight, at a low angle, where streaks show. If the finish is good on the worst-lit pane, it will be good everywhere. If not, adjust dilution or water quality before committing to the full clean.
Key Takeaways
- Keep cleaner in the pH 7-10 band; never below pH 4.
- Ammonia and strong alkali shorten suction-cup life by months.
- Dilute at about 1:100 – more dose means streaks, not cleaner glass.
- Fix hard-water spots by filtering rinse water, not by using acid.
- Always finish with a filtered-water rinse pass.
Not sure what to put in your machine? Ask us for a fluid recommendation for your glass type.
How do you set up a rinse-water loop?
Two stages. A coarse filter catches grit before it reaches the roller, and a fine filter or softener conditions the rinse water. Change the coarse cartridge every 2-4 months and the fine one to the hardness you measure. Test with a cheap TDS pen at the tap; anything above 200 ppm should go through conditioning before it touches glass.
Recirculation is worth it on dry sites. A loop that reuses water for the first pass and finishes with fresh rinse cuts consumption by roughly half. That matters where roof-level water is limited or where a licenced supply is metered. It also keeps the finish consistent between the dirty and clean passes.
What about disinfecting and odour?
Most skylight glass does not need disinfectant. Adding it risks residue and shortens cup life for no visible gain. If odour from droppings is the issue, fix the source – the droppings – rather than masking it with scent. For food-handling buildings, follow the site’s sanitation rules and use a product approved for food-contact surfaces, then rinse thoroughly.
Never mix products. Combining an alkaline cleaner with an acidic descaler produces heat and fumes and can damage the machine’s seals. One product per tank, diluted to spec, is both safer and cheaper than a cocktail that promises everything.
Do you need different fluids for different seasons?
Summer changes the job. Hot glass dries rinse water in seconds, so a slightly richer mix and a faster rinse follow-through stop the tide lines that show on dark glass. Winter works the other way: cold glass and cold water mean slower evaporation but a risk of residue if the detergent does not fully dissolve. Pre-mix in a warm room, not on a freezing roof.
Pollen season is its own case. A sticky yellow film needs a bit more dwell and a second pass; a single fast wet-down smears it. Add one slow pass in spring rather than changing the product. The fluid stays the same, the technique adapts.