Brown marks on fibreglass pool floor

[grungee1]

Hi,Forum newbie here.
I have a saltwater fibreglass pool that has a few small brown marks on the pool floor. There seems to be more appearing each week. The best description I could give is to say they look exactly like the hair pins (or as we call them in Aust. bobby pins) that ladies put in their hair to hold it out of their face. How can I remove them and what are they. I have tried scrubbing with a scouring pad but I dont want to get too violent for fear of damaging the fibreglass. I asked the pool builder a few years ago and he said they might be a fungus and to just scrub them away but I am not having a lot of sucess.
Any advice would be greatly appreciated.

[dynamictiger]

Okay. Could they be hair pins? Hair pins rust and create a brown stain on the fiberglass.

Fiberglass loves acid. One of the methods I use for spot removal is to add a cup down a pipe with the pipe held over the stain for several minutes. After a few applications most stains start to fade. Simply use this to adjust the pH when required and in a few weeks all the stains are treated.

HTH

[Guest]

No, they are not actual hair pins, they just look like them. Do you pour straight acid down the pipe or do you dilute it slightly?

[dynamictiger]

Add the acid neat to the pipe the pool water will dilute it anyway.

HTH

[grungee1]

Yes, of course. That was a dumb thing to say on my behalf wasn't it. Anyway, I'll give that a try and let you know in a few days.
Thanks for you reply