One of the most consistent things we hear from fibreglass pool owners is that the maintenance is easier than they expected. That reputation is well earned. But easier doesn’t mean effortless, and a fibreglass pool that isn’t looked after properly will show it over time.
This guide covers what fibreglass pool maintenance actually involves, what makes it different from maintaining a concrete pool, and what to watch for over the longer term. If you’re looking for a general seasonal maintenance routine that applies to all pool types, our seasonal pool maintenance guide covers that in detail. What follows is specific to fibreglass.
Why Fibreglass Is Easier to Maintain Than Concrete
The key is the gel coat surface. Unlike concrete, which is porous and provides a textured surface that algae and bacteria can grip onto, the gel coat on a fibreglass pool is smooth and non-porous. Algae struggle to take hold, contaminants sit on the surface rather than penetrating it, and routine cleaning is considerably more straightforward.
In practical terms, this means less algaecide, less scrubbing, and lower overall chemical consumption than a comparable concrete pool. Over a season, the difference in both time and chemical costs is meaningful. Over a decade, it’s substantial.
That said, the gel coat is not indestructible, and how well you look after it determines how well the pool holds up over the long term.
Water Chemistry: Getting It Right for Fibreglass
Water chemistry matters for every pool, but there are specific considerations for fibreglass that are worth understanding.
The pH of your pool water should be maintained between 6.8 and 7.4, with an ideal target of 7. While this is the same recommended range for all swimming pools, fibreglass pools are more sensitive to water that remains consistently acidic. If the pH falls below 6.8 for an extended period, it can begin to attack the gel coat surface, causing it to fade, become chalky, or in severe cases, blister.
Free chlorine should be maintained between 1.0 and 3.0 ppm. As a general rule, it is best to keep chlorine towards the lower end of this range, provided the water remains clear, sanitised, and balanced. Maintaining the correct chlorine level prevents the growth of algae and harmful bacteria while protecting the pool finish from unnecessary chemical exposure. We recommend testing your pool water at least twice a week during the swimming season and correcting any imbalance promptly, particularly if the pH begins to fall below the recommended range.
Calcium hardness is another area where fibreglass needs attention. Very soft water, low in calcium, is aggressive and it will leach minerals from any surface it’s in contact with. For fibreglass, this can cause the gel coat to deteriorate prematurely. Keep calcium hardness between 150 and 375 parts per million and top up with calcium chloride if levels fall below that range.
Cyanuric acid, used to stabilise chlorine against UV degradation, should be kept between 25 and 50 parts per million in an outdoor fibreglass pool. Levels above 50 ppm make chlorine significantly less effective and can be difficult to correct without partially draining and refilling the pool.
| Unstabilized Chlorine | 0.3–1.5 ppm |
| Stabilized Chlorine | 1.0–3.0 ppm |
| pH | 6.8–7.4 |
| Total Alkalinity | 80–120 ppm |
| Cyanuric Acid | 25–50 ppm |
| Calcium Hardness | 150–375 ppm |
| Salinity (excluding low salt) | 3500–4500 ppm |
| Total Dissolved Solids | <1500 ppm |
| Phosphates | 0 |
Cleaning the Gel Coat Surface
The smooth surface of a fibreglass pool makes brushing and cleaning easier than concrete, but it does require the right tools and technique.
Always use a soft nylon brush rather than a wire or stainless steel brush. Hard bristles will scratch the gel coat, and scratches create texture for algae and contaminants to grip onto, undermining the key advantage the surface offers in the first place. A soft brush used regularly is far more effective than an abrasive brush used occasionally
For stubborn staining, a specialist fibreglass pool cleaner is the right tool. Standard household cleaners and abrasive compounds should never be used on a gel coat surface. If staining persists despite correct water chemistry and regular brushing, it’s worth identifying the cause before reaching for stronger treatments. Metallic staining, most commonly from iron or copper in the water, requires a dedicated metal sequestrant rather than increased chemical doses.
Waterline staining is common on all pools and particularly visible on lighter fibreglass finishes. A small amount of pool tile and vinyl cleaner applied to the waterline with a soft cloth will address most surface build-up. Stay on top of it regularly rather than leaving it to accumulate.
What to Avoid
A few things that are harder to undo than to prevent in the first place.
Draining a fibreglass pool completely should only be done when necessary and only after taking professional advice. Fibreglass shells are designed to hold water, and the hydrostatic pressure from groundwater beneath the pool can cause a shell to float or shift if it’s emptied without proper precautions. This is rarely an issue if the pool is maintained correctly and never needs draining, but it’s worth knowing.
Copper-based algaecides, widely available and effective in concrete pools, can cause persistent blue-green staining on fibreglass surfaces. Use algaecides that are specifically formulated as safe for fibreglass, and check the label before adding anything new to the water.
Allowing pH to drift below 6.8 consistently, as mentioned above, is the single most damaging thing for a gel coat surface over the long term. A good digital test kit and a consistent testing routine costs very little and prevents problems that are genuinely expensive to fix.
Longer Term Care: Keeping the Gel Coat in Good Condition
A fibreglass pool that is properly maintained should hold its surface well for many years without needing significant intervention. But there are a few longer-term considerations worth planning for.
Oxidation of the gel coat can occur over time, particularly in pools with significant UV exposure. The surface can begin to look dull or faded rather than having its original lustre. A fibreglass pool polish, applied every few years, restores the surface and provides a degree of protection. This is a straightforward job that most pool owners can carry out themselves.
Osmotic blistering, sometimes called gel coat blistering, is a condition that can affect fibreglass pools where water penetrates the gel coat and causes small bubbles to form beneath the surface. It’s more common in older or lower-quality shells and can be caused by consistently poor water chemistry. A quality shell from a reputable manufacturer, combined with correct water chemistry, makes this extremely unlikely. Aqua Technics pools are manufactured using PoolColour Guard, which acts like a sunscreen for your pool, but also has an antimicrobial surface for higher chemical and algae resistance. You can find out more about the range on our Aqua Technics pools page.
If blistering does occur, it should be assessed and repaired by a professional. Left untreated, it can spread and become a more significant repair job.
When to Call in Professional Support
Most fibreglass pool maintenance can be managed by the pool owner once the right routine is established. There are times, though, when professional support makes sense.
Opening and closing the pool at the start and end of the season is a good time to have a professional eye on the equipment, water chemistry, and shell condition. Any unusual staining, surface changes, or equipment behaviour that you can’t diagnose and resolve yourself is worth getting looked at promptly rather than leaving.
XL Pools offers a pool maintenance service for owners across Kent and the South East, covering everything from routine care to seasonal openings and full equipment checks. If you’d like to hand the maintenance over entirely, or just want a professional check-in each season, get in touch with our team to find out more.
