I have a fiberglass pool and noticed this on our stairs. I scrub pretty hard and it stays. How can you tell if it’s algae vs a stain?
Black algae?
- Thread starter RHanna
- Start date
- Jun 22, 2014
- 52,038
- Pool Size
- 17888
- Surface
- Fiberglass
- Chlorine
- Salt Water Generator
- SWG Type
- CircuPool RJ-45 Plus
A couple things you could do to help us narrow it down:
1 - Post a new full set of water test results. You can show them here and/or in your Poolmath log since it's linked.
2 - Try to rub a Vitamin C tablet on the stained area. It the Vitamin C tabs removes a stain, it's iron. On a well?
Let's start there and see where it takes us.
1 - Post a new full set of water test results. You can show them here and/or in your Poolmath log since it's linked.
2 - Try to rub a Vitamin C tablet on the stained area. It the Vitamin C tabs removes a stain, it's iron. On a well?
Let's start there and see where it takes us.
I’ll run a full set of tests tomorrow morning. City waterA couple things you could do to help us narrow it down:
1 - Post a new full set of water test results. You can show them here and/or in your Poolmath log since it's linked.
2 - Try to rub a Vitamin C tablet on the stained area. It the Vitamin C tabs removes a stain, it's iron. On a well?
Let's start there and see where it takes us.
Katodude
Silver Supporter
- Aug 22, 2017
- 3,004
- Pool Size
- 15000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Hayward Aqua Rite (T-15)
Take a wooden toothpick or a bamboo bbq skewer and try to pick at it. See if you can pick out a spot or two and smear it on a piece of paper. If it smears green its black algae
I just logged it on poolmath but I have no idea if the CYA reading is correct. I really hate that test. I briefly look at the bottom with my back to the sun and I feel like I could see the dot until 20 really but I don't see how my CYA could possibly be that low. I just added about 1 gallon of instant CYA about a month ago so that should have raised it 16.
- Jun 22, 2014
- 52,038
- Pool Size
- 17888
- Surface
- Fiberglass
- Chlorine
- Salt Water Generator
- SWG Type
- CircuPool RJ-45 Plus
Your Poolmath FC level is nice today, but not sure if it was maintained that way consistently. As noted above, have you tried scraping the spots off and rubbing on a paper towel? If the stain appears embedded, try rubbing with a Vitamin C tablet?
My FC was higher for a while until I turned the heater on and raised the temp. I think the FC started to burn off faster so I had to increase my SWG percentage.
Haven't had much time to work on the pool. We had a tornado warning this morning and thunderstorms so I might be able to see over lunch.
Haven't had much time to work on the pool. We had a tornado warning this morning and thunderstorms so I might be able to see over lunch.
A few more pics. I'm not sure I've been able to scrap anything off to see if it was green. I think I'll have to go buy some ascorbic acid
I bought some ascorbic acid and rubbed the spots and nothing happened. I tried again to scrap something, this time with bamboo skewers but nothing came off.
My understandsing is that its very hard to imagine black algae in a fiberglass pool as there is no way for the roots of the algae to "take hold" in the smooth surface. It could be regular algae, stains, dirt, metal stains......
Maddie
Maddie
- Jun 22, 2014
- 52,038
- Pool Size
- 17888
- Surface
- Fiberglass
- Chlorine
- Salt Water Generator
- SWG Type
- CircuPool RJ-45 Plus
Yeah, if the ascorbic acid did nothing, that should rule out iron. There are 3 more possibilities I can think of:
1 - Organic; try rubbing a chlorine tablet on the spot, but don't let it just sit. Keep it moving.
2 - Put a little dry acid in a thin sock and rub it to see if it's copper
3 - Possibly cobalt staining's. We'd have to come back to that one if needed.
1 - Organic; try rubbing a chlorine tablet on the spot, but don't let it just sit. Keep it moving.
2 - Put a little dry acid in a thin sock and rub it to see if it's copper
3 - Possibly cobalt staining's. We'd have to come back to that one if needed.
I tried a chlorine tablet and it didn’t do anything. I added dry acid and rubbed with a sock but it didn’t do much. Then I poured the dry acid on a spot and let it sit for a couple of minutes and that seemed to get one spot ok. It looks like it’s spreading and it seems to stay in the creases of the pool. This is super frustrating, I don’t know what it could be. I haven’t added much water this year and I haven’t even fertilized the lawn yet so if it’s metal I have no idea where it came from.
I had read that black algae was unlikely in a fiberglass pool and the chlorine tablet didn’t do anything
I had read that black algae was unlikely in a fiberglass pool and the chlorine tablet didn’t do anything
ok, your FC is right on the border.....raise it up and keep it about 9-10 and see if over time and with brushing that will help. Its safe to swim in, so don't worry.
Has anyone added cheap algaecides or used copper in the pool?
Maddie
Has anyone added cheap algaecides or used copper in the pool?
Maddie
I'm the only one that works on it so no, I've never used algaecide or anything with copper in it as far as I know.ok, your FC is right on the border.....raise it up and keep it about 9-10 and see if over time and with brushing that will help. Its safe to swim in, so don't worry.
Has anyone added cheap algaecides or used copper in the pool?
Maddie
I added 2 gallons of instant CYA yesterday because my CYA was so low and I'm impatient.
I’m a guy but that’s ok, I’m used to it with a last name Hanna.hehehehe....you and me both, sista!
Well geesh~ Ya should have typed RHanna then 
I'll try to remember your gender, but I can't promise, ok mister?
I'll try to remember your gender, but I can't promise, ok mister?Similar threads
