fiberglass pool stains HELP!

this year has been a nightmare with pool stains....entire pool completely covered by a rust/orange coat.
This happend after I had the ocurrence of shocking the pool with clorax to open it.
I was able to remove completely using citric acid...24hrs overnight
and the pool looked great. I then added a Metal out product(s) to prevent it from happening.
All pool parameteres are perfect.
The stain came back!!!!
what can I do to remove what is staining the pool after treating with citric acid?
should I use KDF-85 and Birm..... to filter the water that is in the pool?
How can I prevent this fromhappening?
thank you!