How to clean fibreglass pools

November 10, 2023

The attractive gloss of a fiberglass pool tells you that it is pristine and grime-free. After about a month of enjoying your new pool, you start to notice dark rings forming subtly around its water line. Don’t be disillusioned that it is just a shadow cast by the sun. That stain is not going away on its own. Here are some factors to consider if you want to remove that black stain:

  1. Pools made of fiberglass will always stain. A pool made of plaster is porous. A pool made of fiberglass is not. Because a fiberglass pool is not porous, it does not become rough and etched. You don’t have to worry about algae growth, stubborn stains, or pool toes.
  2. Stains do not magically appear. Stains can appear in fiberglass pools. They are often caused by imbalanced minerals or chemicals, foreign objects, or high amounts of metals. Sun block and suntan oils can cause that bathtub ring.
  3. Water balance is crucial. If you test your water daily, you maintain good water balance. Make sure to maintain a pH balance of 7.2 to 7.4. Its alkalinity should be between 80 and 100 parts per million. Make sure you maintain calcium hardness between 200-400 ppm and chlorine levels at least 1 ppm. Stains start to develop once these numbers go haywire. Just maintain a well-balanced pool universe and it will be stain-free.

But what happens if your fiberglass pool is already stained? How can you remove them? Here are some of the steps to consider:

  1. To remove rust. Rub a vitamin C tablet on the stain until it is gone. If the rust is caused by contact with metal, it should disappear immediately. You can use a brush with soft bristles to remove any excess rust. If you suspect a rust infection, place ascorbic acid powder in the pool filter.
  2. To remove light bathroom ring stains. Apply commercial pool tile cleaners on those light pool stains to remove them. You can also use sponges, liquid detergent (or soap) and warm water.
  3. To remove heavy bathroom ring stains. A mixture of water and oxalic acid is an effective way to remove heavy bathroom ring stains. After running your pool filter, pour the chlorine.
    Make sure to bring back the pH balance of the water after cleaning your pool. It is always better to clear out the light pool stains as soon as you see them. Do not leave them for a long time, or they will become hard stains, which are difficult, costly, and damaging to remove.