Conflicting "experts" and The Mystery Stain

[MWave36]

Hello all,

I'm a wanna-be do-it-yourselfer trying to figure out if I should (or even can) de-stain my 1,560 ft3 fiberglass pool or paint it. Here's my dilemma:

First, what the heck is this?






This pool has been empty for about five years. I had it acid washed when I bought the property in 2007 but drained it after three years of little usage (with the intent to someday fill it in and convert it to a putting green – remarkably there are no lumps or cracks). The stain has been there since the pool was drained. It was textured and threw off a lot of powder when rubbed. After a recent chlorine wash the surface now feels smooth and clean and it appears this is a discoloration of the fiberglass itself. However, when I rubbed a spot with nothing but a wet rag I was able to remove about 50% of the upper (lightest) of the four layers (again, this was after the professional chlorine wash). But even using an SOS pad had very little affect on the middle or bottom (darkest) layers. The pool guy now tells me there's nothing more that can be done to lighten the stain*, but I'm finding so many products and methods that can supposedly remove any type of pool stain that exist (usually one product per specific stain type, but some claim their single product is a pool stain panacea). Everything I find online that looks like this stain is either on a different surface type or only explains what to add to the water of a filled pool.

So, is there anything I can rub on a dry stain of this type to remove it?

My challenge with learning how to paint it is that so far I've read 10 online articles and asked the guy down at Leslie's and five say I need a primer coat before applying the epoxy pool paint, four say I only have to lightly sand it, one claims I only need to be sure its clean, and one instructed me to get another acid wash first to "help the paint stick".

So, on a fiberglass pool in this condition, do I need a primer coat or light sanding?

Finally, I'm in Las Vegas where it's going to be over 100° literally every day for at least the next 4-5 weeks, and 112° is predicted for next weekend when I planned to do the job.

So, what happens when you paint epoxy on the same surface you could fry an egg on?

Thanks guys. I appreciate any guidance you can offer.

Len

* But says he'll paint it $1,200.

[Denniswiseman]

Can't help with the painting
But test the stain first of all with bleach to see if it's organic (algae)
Then test with hydrochloric acid to see if it's inorganic (metal)

[mknmike]

Could stains like this be from moisture getting in from the back side? Like what if there was a pool leak and it created muddy water on the other side?

I’m curious because on the side of my pool where the tile fell off, I notice a slightly similar stain at the corner where the wall meets the floor.

[Teapot1]

Could stains like this be from moisture getting in from the back side?.

Short answer no.

[Teapot1]

Can't help with the painting
But test the stain first of all with bleach to see if it's organic (algae)
Then test with hydrochloric acid to see if it's inorganic (metal)

It looks a lot like iron staining, I would go with vitamin C rather than hydrochloric or even or oxalic acid first.
Epoxy pool paint is generally rubbish but that said I havent repainted a fibreglass pool but on concrete it soon cracks and flakes despite really good prep.