New Marbelite pool

[venter]

Recently re marbelite my pool and not very happy with the service.On the day of the job and after the pool was finished,it rained a bit and now the marbelite on the sides seems to have some marks of the cement they used for the mosiac tiles.
How can this be removed without damaging the lining or must the company come and fox this.
They told me to add some acid to the pool and then brush but the acid should take care of this.