Stain Identification

How to Identify and Remove Stains in Your Fiberglass Pool

A fiberglass pool is a significant investment in your home, and while they are known for their durability and low-maintenance surface, fiberglass pools can occasionally develop stains.

Understanding the cause of discoloration is the first step toward restoring your pool’s pristine finish.

This guide will walk you through some of the types of stains that can appear on your fiberglass pool, how to prevent them, and the correct methods for removal. By following these steps, you can keep your Tallman Pool looking beautiful for years to come.

Understanding Types of Fiberglass Pool Stains

All pool stains fall into two primary categories: organic or inorganic.

Identifying which type you are dealing with is crucial for effective removal. You can use a stain identification kit that uses testing agents added to the water to determine the exact nature of the stain.

Organic Pool Stains

Organic stains come from natural materials that find their way into your pool. These are often the most common types of stains pool owners’ encounter.

Common sources of organic stains include:

Leaves

• Berries and other fallen fruit
• Dirt, mud, and Pollen
• Algae (while not technically a stain, certain types like black algae can leave behind stain-like spots)

These stains typically appear as green, brown, or tan blemishes on the pool surface.

Inorganic Pool Stains

Inorganic stains are caused by metals or mineral deposits in your pool water. While they are less common, they can still occur.

Metal-Based Stains

These stains happen when dissolved metals in the water oxidize and attach to the pool’s gelcoat.

Common sources and their resulting colors include:

• Iron: Orange, brown, or tan stains.
• Copper: Green, blue, or teal stains.
• Manganese: Brown, black, or purple stains.

Cobalt Stains

Cobalt stains manifest as black spots on the pool’s surface. Technically, this is not a stain but a reaction. It occurs when water passes through the gelcoat and reacts with the underlying resin, creating a black byproduct.

Calcium Scaling

Scaling is not a stain; it is a common surface issue that can look like one. It is a buildup of calcium crystals on the pool’s surface and can appear as spots, streaks, or even stripes. If left untreated it can damage your gelcoat surface.

There are two main types of calcium scaling:

Calcium Carbonate:

• Cause- High pH, or Alkalinity, oversaturation of calcium hardness.
• Appears as white, flaky deposits.

Calcium Silicate:

• Cause- Long-term imbalance of water chemistry (high calcium hardness and PH)
• A white or grayish buildup that is difficult to remove.

To differentiate between them, you can apply a drop of muriatic acid to a small, dry area of the scale. Calcium carbonate will foam and react, while calcium silicate will show no reaction.

How to Prevent Fiberglass Pool Stains

Prevention is always more effective than treatment. By adopting a consistent maintenance routine, you can significantly reduce the likelihood of stains forming on your pool surface.

Maintain Proper Water Chemistry

Balanced water is the foundation of a healthy, stain-free pool. Follow the Tallman Pools Use-and-Care Manual.

Regularly test your water and keep the following levels within their ideal ranges:

• pH: 7.2 – 7.6
• Total Alkalinity: 80 – 120 ppm
• Chlorine: 1.0 – 3.0 ppm
• Calcium Hardness: >120 ppm

Consistently balanced water prevents the conditions that allow metals to fall out of solution and minerals to form scale.

Regularly use a cleating agent /scale, and metal control.

*Never use products that contain calcium hypochlorite (cal-hypo). Cal-hypo can introduce unnecessary calcium into the water, contributing to scale formation.

Clean Your Pool Regularly

Routine cleaning removes organic debris before it has a chance to settle and stain the surface.

• Skim the surface daily to remove leaves, bugs, and other floating debris.
• Vacuum the pool floor and walls weekly.
• Brush the pool surface, including steps and benches, to dislodge any early signs of buildup.
• Promptly remove any foreign metal objects, such as hairpins, toys, or tools, which may have fallen into the pool.

How to Remove Stains from a Fiberglass Pool

If a stain does appear, address it as soon as possible. Before attempting any chemical treatments, try wiping the spot with a soft cloth or sponge.

Never use abrasive tools or harsh chemicals not specifically designed for fiberglass pools, as they can permanently damage the gelcoat.

If gentle wiping doesn’t work, follow the steps below based on the stain type.

Removing Organic Stains

Organic stains are typically the easiest to remove.

1. Brush Vigorously: Use a pool brush to scrub the stained area. In many cases, this is enough to lift the stain.
2. Use a Stain Eraser: If brushing is not effective, use a stain eraser designed for swimming pools. Gently rub it on the spot until the stain disappears.
3. Be Patient: If a faint stain remains, it will often fade and disappear on its own over a few weeks to a couple of months with proper water chemistry and regular sanitization. If it persists, it may be time to consult a pool professional.

Removing Inorganic Stains

Removing metal stains and mineral deposits requires a more targeted approach.

Metal Stains

For small, isolated metal stains:

• Rub a vitamin C tablet directly onto the stain. The ascorbic acid in the tablet creates a chemical reaction that can lift the metal from the gelcoat.

For larger or more widespread metal stains:

• Prepare the Water: Lower your pool’s chlorine level to 0.0 ppm and adjust the pH to 7.2.
• Add Ascorbic Acid: Turn on the pool filter. Add ascorbic acid (the main component of vitamin C) to the water at a rate of approximately one pound per 10,000 gallons. Distribute it evenly around the pool.
• Circulate: Allow the pump and filter to run for 24 hours. The stains should disappear during this time.
• Sequester the Metals: After the stains are gone, add a metal sequestering agent to the water. This product binds to the dissolved metal particles, preventing them from re-staining the surface.
• Re-balance: Test and re-balance your water chemistry to its proper levels.

Cobalt stains

• Treat with Jack’s Magic Product- The Iron, Cobalt, & Spot etching stuff

Calcium Scaling

• Calcium Carbonate: You can remove these white, flaky deposits with a pool stain eraser or a scaling treatment product formulated for fiberglass pools.
• Calcium Silicate: This type of scale is much more difficult to remove. Adding a dedicated pool-scaling treatment to the water is the best course of action, though results will be gradual. For faster removal, it is best to contact a qualified fiberglass service technician.

*Jack’s Magic and Poolstainremovers.com offer products for scaling