Stains on Fiberglass pool

[Janmcm5656]

I need help with stains on our pool. 18000 gallon fiberglass with cartridge filter. In April it had some staining so I put united chemical super stain treat in it following the directions. I used it because the company that made the pool used it several years ago and it worked great and I haven't had any issues since. We went out of town for about 5 days, when we got back it was a little green so I got algecide and put it in and shocked it. The stains came back. So I got Leslie's stain remover and metal free followed directions also put culator in skimmer. Looked good for a few days slowly raised Chlorine did not shock but stains came back. Got another super stain treat put it in waited 4 days added united chemical pool stain treat . Had water tested it showed copper and phosphorus no iron. Added metal free waited til next day added Seaklear phosphorus remover. Had water tested no iron, copper or phosphorus. But chlorine was low .5 because you are not supposed to shock. So I raised Chlorine to 2. Now stains are back. Also have cleaned cartridge filters 3 times during this time. I feel like I am on an endless circle where I either have to keep the stains or cannot have Chlorine in the pool. Last night I took vitamin c tablet to see if it would remove the stains and yes they come right off . Any help would be appreciated.

[Teapot]

Yes, the pool shops have you in an endless cycle.
Problem is cartridge filters cannot remove iron.
Algaecide will not kill algae! Pool shop lies. Only a copper based algaecide could help but stay away.
Metal out is just a sequestrant and does not take anything out! It just temporarily binds it up as you have found. CU later works but only removes small amounts so you need to keep buying them.

These Polly balls seem to do something to remove iron but I haven't personally tested them. I have tested Dr Dryden's Activate glass filter media and confirm that does remove iron if you follow the procedure. If iron is in your supply water consider changing to something that actually works

[Janmcm5656]

But my water has never shown that it has iron. I think the only reason for the copper was from the algecide. So is it even iron or could it be something else?

[Teapot]

It's a little tricky as when you see iron staining it's dropped out of solution so often doesn't show up on tests. If you add sequestration it binds to the iron and often doesn't show up in tests.
Using a reducing agent like ascorbic acid puts the iron back in solution (removes the stain) but when you add chlorine you re oxidise it and it stains again.
Your description sounds like iron to me.

[Janmcm5656]

What is in culator and can you buy it in larger amounts somewhere else? Is there any type of filter that can be added to return lines to actually remove the metals?

[Teapot]

Curator is a anionic polymer, other than that it's secret.
These Polly balls can it seems remove some iron and may help. Personally I use Dr Dryden's Activate glass filter media and have demonstrated the iron removal in front of customers.

There is one thing I overlooked the other day as you say no metals in test results. Have you added any bromine products like jack's magic etc? Sometimes chlorine action with bromine can turn brown.

[Janmcm5656]

Not before yesterday. Yesterday I cleaned filter cartridge and added Jacks magic saffire. Can we use the Dr Dryden's with a cartridge filter?