Step 1: Regularly monitor the water and the liner
Step 2: Make the diagnosis
Step 3: Lower the pH of the water to 6.8 and stop the filtration.
Step 4: Case 1: Remove a recent isolated brown stain
Step 4: Case 2: Remove larger and older brown spots
Step 5: Raise the pH and run the filtration system
Step 6: Replace your pool liner
Despite a well-maintained pool and clear water, unsightly brown stains may appear, either on the sides of the liner or on the bottom of your pool. Removing brown stains on a liner can be either very easy or much more delicate when the stains are due to micro-fungi embedded in the masonry behind the liner. Even if the result is not definitive, you can try the following method, especially since you probably have most of the material you need.
1. Regularly monitor the water and the liner
Removing brown stains on a liner is all the more difficult as the damage is old and extensive.
Keep water always clear so that you can easily spot any unusual stain.
Regularly check that the water parameters are within the recommended standards: the pH, in particular, should be between 7 and 7.6 (7.8 maximum).
You should take action immediately if you notice any brown spots on the liner.
2. Make the diagnosis
Brown stains on a liner can be due to a deposit of dead algae on the liner or micro-fungi‘s installation behind the liner in the masonry.
To establish the diagnosis, vigorously brush the brown stains:
- If they disappear, they are dead algae, and your problem is solved.
- If the stains do not fade, they are probably micro-fungi embedded in the masonry behind the liner.
The liner of a swimming pool is not a completely waterproof material – especially when it ages, it can have some porosity: moisture can settle between the liner and the walls or the bottom of the pool, causing the incrustation of coloured micro-fungi in the masonry.
3. Lower the pH of the water to 6.8 and stop the filtration
To remove the brown stains that appear behind the liner, it is necessary in all cases to lower the pH of the water to 6.8, which will dilate the pores of the liner and make the masonry more accessible for treatment.
– Measure the pH of the water using your pH tester.
– If the pH is higher than 6.8, add pH minus.
– Check the pH with your pH meter: – it should then be equal to or below 6.8
– Stop filtration.
4. Case 1: Remove a recent isolated brown stain
If the brown spot is isolated and recent, you can try the following method:
- Put on gloves.
- Use a slow chlorine roller.
- With a mask, dive into rubbing the stain with the chlorine pad. If the development of the micro-fungi is recent, there is a chance that the stain will fade.
- If necessary, repeat the operation if the stain reappears.
4. Case 2: Remove larger, older brown stains
Pour calcium hypochlorite (or only bleach) in a watering can and pour it as close as possible to the stains.
If the stains are at the bottom of the pool, use a rigid PVC hose and pour the bleach into the hose after positioning it over the stain.
Good to know: calcium hypochlorite can be found in pool supply stores. You can replace it with bleach, which has almost the same composition. Both are effective against bacteria, viruses and fungi.
5. Raise the pH and turn the filtration on and off
- Regardless of the method used (chlorine pebble or bleach), leave the filtration off for one hour.
- After one hour, turn the filtration back on.
- Raise the water’s pH to a maximum of 7 or 7.2 (the pH of pool water should be between 7 and 7.4, however, with a relatively low pH you can expect a lower recurrence of brown spots).
- Run the filtration for 72 hours non-stop.
- Finish with a filter wash.
6. Replace the liner of your pool
Unfortunately, you cannot skip the fear that the micro mushrooms will return. So, you can repeat the treatment to remove the brown spots on the liner.
The only definitive solution would be to empty the pool and remove the liner to treat behind if they persist.
Caution: when the time comes to change the liner of your pool, it will be essential to carefully disinfect the pool’s walls and bottom before installing the new liner.
And, that’s it. You are now done removing brown stains on your pool liner. In case the above steps seem too complicated for you, some specialist companies out there will do the job for you after evaluating your pool. Look for a few quotes before making up your mind, and remember to share your experience below.
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