Removing ' Water Level' dirt/discolouration ?

[Robin]

Advice please !

We have a fibreglass pool . Our previous pools have all been 'traditional' pools with 'plastic' liners.

I have great difficulty removing the staining at the water level around the sides of the fibreglass pool.

I have the PH/CL levels correct.
Our water is NOT high in calcium.

I have tried the usual products .

What would you guys recommend please ? Is this usual with fibreglass pools perhaps ?
Our older 'traditional' pools [ with a liner ] were much easier to clean.

Much obliged for any advice ,

Thanks ,

Robin. [ S.W.France - British ex-pat ]

 

[PoolGuyNJ]

A Mr. Clean Magic Eraser and a Scotch Brite pad usually get it done quite nicely.

Scott

 

[Robin]

Scott , good morning from France.

I'm very much obliged , thanks,

Robin.

 

[Bama Rambler]

Robin, can you provide us with a full set of test numbers?

pH
FC
CC
TA
CH
CYA