A citric acid wash is most effective on a swimming pool that has been cleaned with all debris removed after it is drained.
Citric acid wash for pools.
An acid wash would likely remove it you can test by lowering the water level down below the first step and pouring a 50 50 acid water mixture from a flower watering can over the step scrubbing briefly and hosing off within 60 seconds.
If it works an acid wash would be a good next step.
Pour water over any remaining.
Mix it gently with a mixing stick if you need to.
Bosh chemical vanish pool spa stain remover 2lbs natural safe citrus based works excellent on vinyl fiberglass and metals removes rust and other tough stains.
Spray down the sides of the pool and make sure the entire surface is wet.
Dispose of what you pumped as the acid can kill frogs fish and plants.
9 kg of soda.
Use a half a pound of vitamin c for every 10 000 gallons of water.
When you get the ascorbic acid in the water you can turn on the pool pump and let the filters circulate the water for about a half hour.
Wet the sides of the pool.
Pump the mixture into a bowl using a submersible pump.
In your five gallon bucket add one gallon of acid to one gallon of water never the other way around.
You will need to use 2 lb.
Rinse out the bowl.
The acid wash is applied from a watering can used for flowers.
For citric acid for pools.
Fill the can with 1 gallon of water and then add 1 gallon of citric acid always in that order.