Orange spots (possibly rust?) on fibreglass pool surface

[MoogMan]

Hi there.

So I have some what I can only assume are rust spots on the fibreglass pool steps (where the robotic vaccum doesn't get to). I brush these daily but had missed a few days.

Scrubbing and cleaning do not touch them. I have tried the vitamin c tabs trick (15 in a sock crushed and then held on for 3/5mins) but no use.

There has been work performed fairly close to the pool, so I assume these are from metal shavings or something. However I believe only aluminium was being cut and obviously it shouldn’t rust. Perhaps it has reacted with the salt?

Anyway. Your advice would be greatly appreciated. What are my options?

Pool is tested with Taylor kit and balanced.

FC 6
PH 7.6
CYA 60
TA 60
CH 250



Thanks in advance!

 

[Mdragger88]

Been fertilizing? Some could have blown in.
You’re correct, Aluminum doesn’t rust/turn orange & the salt should be of no consequence.
You can try some bar keepers friend (oxalic acid) although you may need to lower the water to get to it better & have it be effective without losing at all in the pool. Also a magic eraser or both if you haven’t already. You could try putting it on the magic eraser & holding it on the stain a few minutes - wear gloves. The cream may stay together better than the powder.
Some have had success with clr but it nor vit c does nothing for my bathtub & the bkf works.
Let’s see what @Texas Splash says

 

[mknauss]

In another thread you state you used Milorganite in the area. Since that comes from Wastewater treatment effluent, it can have any number of metals or or other constituents in it.
Follow what Mdragger stated above, likely just need to scrub it off.

 

[JamesW]

Possibly cobalt, but that should not happen on a relatively new pool.

 

[Mdragger88]

In another thread you state you used Milorganite in the area. Since that comes from Wastewater treatment effluent, it can have any number of metals or or other constituents in it.
Follow what Mdragger stated above, likely just need to scrub it off.

Milorganite also definitely contains iron-