Black Stains Fibreglass
- Thread starter denniswiseman
- Start date
- Jun 22, 2014
- 47,783
- Pool Size
- 17888
- Surface
- Fiberglass
- Chlorine
- Salt Water Generator
- SWG Type
- CircuPool RJ-45 Plus
Hello Dennis! 
Let me ask you this first .... do you have your own test kit over there, and if so, what kind is it? We really need a full set of water test result to help pinpoint what the staining might be. I know some testing products are hard to obtain away from the U.S., but knowing those chemistry levels is extremely important to differentiate between the different causes (i.e. algae, calcium, etc).
Let me ask you this first .... do you have your own test kit over there, and if so, what kind is it? We really need a full set of water test result to help pinpoint what the staining might be. I know some testing products are hard to obtain away from the U.S., but knowing those chemistry levels is extremely important to differentiate between the different causes (i.e. algae, calcium, etc).Hi Pat
I use the Aquachek meter and strips as test kits aren't readily available
Chlorine 3
PH 7.4
TA 120
I haven't had this problem before and the pool is checked regularly
I use sodium hypochlorite 14/15% and reduce my TA with Muriatic acid and raise the PH with aeration
I use the Aquachek meter and strips as test kits aren't readily available
Chlorine 3
PH 7.4
TA 120
I haven't had this problem before and the pool is checked regularly
I use sodium hypochlorite 14/15% and reduce my TA with Muriatic acid and raise the PH with aeration
- Jun 22, 2014
- 47,783
- Pool Size
- 17888
- Surface
- Fiberglass
- Chlorine
- Salt Water Generator
- SWG Type
- CircuPool RJ-45 Plus
A couple important items missing are CYA (stabilizer/cyanuric acid) and CH (calcium hardness). The CYA will tell us what your FC level should be, and the CH would indicate any irregularities that may cause calcium staining. I'm afraid I'm not real familiar with the Aquachek meter, and strips don't have much of a good reputation around here. 
But I understand your options are limited. You might however want to check about trying to get the Taylor K-2006C on eBay. I've heard some folks overseas have been able to get it that way. My initial thought was that you have a type of algae on those walls, but I would expect your FC to drop rather quickly if that was the case. Sometimes we get that black scum line appearance around the edges of the pool and in the skimmer, but I've not seen that same reaction below the water and on the walls like yours. Since you don't have a CYA listed (not sure if you can test for it), you might at least try increasing your FC to around 6-8 ppm for a few days to see if that changes anything. If you have a chlorine tablet, try rubbing it around on one of the walls for a couple minutes, careful not to keep it in one place too long. If the black fades or disappears, you know it's organic and a higher FC level would be required. You can refer to the SLAM page (link below) for more details on that process. I hope this info helps give you some direction and ideas next.
But I understand your options are limited. You might however want to check about trying to get the Taylor K-2006C on eBay. I've heard some folks overseas have been able to get it that way. My initial thought was that you have a type of algae on those walls, but I would expect your FC to drop rather quickly if that was the case. Sometimes we get that black scum line appearance around the edges of the pool and in the skimmer, but I've not seen that same reaction below the water and on the walls like yours. Since you don't have a CYA listed (not sure if you can test for it), you might at least try increasing your FC to around 6-8 ppm for a few days to see if that changes anything. If you have a chlorine tablet, try rubbing it around on one of the walls for a couple minutes, careful not to keep it in one place too long. If the black fades or disappears, you know it's organic and a higher FC level would be required. You can refer to the SLAM page (link below) for more details on that process. I hope this info helps give you some direction and ideas next.Hi Pat
I've ordered the recommended test kit
The water level has dropped a bit, can I rub some liquid chlorine onto the stain above the water level to test
I've ordered the recommended test kit
The water level has dropped a bit, can I rub some liquid chlorine onto the stain above the water level to test
- Jun 22, 2014
- 47,783
- Pool Size
- 17888
- Surface
- Fiberglass
- Chlorine
- Salt Water Generator
- SWG Type
- CircuPool RJ-45 Plus
You could try that, or perhaps try it a little diluted (50/50) first to be safe. Rinse well after you've tried it to see if it had any effect. Good job ordering one of the recommended kits. Makes a HUGE difference. Have a nice weekend.
I poured a lot of sodium hypochlorite 13-15% into the skimmer weir and left overnight with the pump off. There was no difference to the staining. It wasn't even soft to scrape or brush off.
The Test kit could take 3 weeks to get here
The Test kit could take 3 weeks to get here
- Jun 22, 2014
- 47,783
- Pool Size
- 17888
- Surface
- Fiberglass
- Chlorine
- Salt Water Generator
- SWG Type
- CircuPool RJ-45 Plus
Wow. Okay then, perhaps not organic. One other thing you might try. Put some muriatic acid in a spray bottle or maybe on the end of a brush and put a small amount on the black material that is exposed above the waterline. No need to let it sit for real long, and of course be very careful with safety (skin and eyes). Rinse the area after the test. But I would be curious to know if there is any reaction when applied (i.e. bubbling). I will be very curious to see what your test results show when your kit arrives.
Greetings, Dennis and welcome.
Did the staining suddenly occur, eg after shocking/slamming, or has it evolved over time?
What is your water makeup source? Are you on a well?
Do you use metal sequestrants? If so, do you maintain same weekly/monthly? Or is the pool new to you?
Do you normally use Algaecides that contain copper?
That *could* be maganese staining, or copper staining that has partially reacted to oxidization (was it a different color before?)
I don't know if you can readily obtain a "jacks magic stain ID kit" -- if you can, that may help sleuth out the best treatment route.
If you can crush up some vitamin c (ascorbic acid) and hold it in the pool against a stain for a few minutes, please tell us if it lightens or turns blackish. That might get us started.
Did the staining suddenly occur, eg after shocking/slamming, or has it evolved over time?
What is your water makeup source? Are you on a well?
Do you use metal sequestrants? If so, do you maintain same weekly/monthly? Or is the pool new to you?
Do you normally use Algaecides that contain copper?
That *could* be maganese staining, or copper staining that has partially reacted to oxidization (was it a different color before?)
I don't know if you can readily obtain a "jacks magic stain ID kit" -- if you can, that may help sleuth out the best treatment route.
If you can crush up some vitamin c (ascorbic acid) and hold it in the pool against a stain for a few minutes, please tell us if it lightens or turns blackish. That might get us started.
Firstly
I topped up the pool shortly after checking but I pulled out the flap (and broke it) from the skimmer weir and poured muriatic acid on it. The stain disappeared immediately (no bubbling)
Secondly
It seems to have evolved over time
We are on mains water supply and the water is hard
I don't think i've used metal sequestrants
The amount of algaecide I use is negligible
I don't think it was a different colour before
I have sent an email to Jacks Magic to see if they have a UK agent
I will get some ascorbic acid to test
I topped up the pool shortly after checking but I pulled out the flap (and broke it) from the skimmer weir and poured muriatic acid on it. The stain disappeared immediately (no bubbling)
Secondly
It seems to have evolved over time
We are on mains water supply and the water is hard
I don't think i've used metal sequestrants
The amount of algaecide I use is negligible
I don't think it was a different colour before
I have sent an email to Jacks Magic to see if they have a UK agent
I will get some ascorbic acid to test
That was my first thought too.
Dennis, does your local pool store offer any testing for metals? Could you bring a water sample in and have them check for them? There is a test kit available here but not sure about there.
Yip
Hi All and thanks for your input
We don't have pool stores here. I suppose the market isn't big enough
Lo-Chlor Black algae killer was put in after the staining
I have already contacted Jacks Magic Stain Identification Kit regarding a local distributor or retailer
We don't have pool stores here. I suppose the market isn't big enough
Lo-Chlor Black algae killer was put in after the staining
I have already contacted Jacks Magic Stain Identification Kit regarding a local distributor or retailer
Dennis, can you please add details to your profile signature line so that we know what kind of surface etc. you're treating?
Another tester just had success on copper stains that had turned black using muriatic acid with the tool I will link below...this is likely only a suitable approach for plaster...and would still require some metal sequestrant, i suspect...
Not especially cheap, but it seemed to work well for him:
Amazon.com: Purity Pool UAW Underwater Acid Wash Set: Patio, Lawn Garden
(Since the MA worked on it.)
Another tester just had success on copper stains that had turned black using muriatic acid with the tool I will link below...this is likely only a suitable approach for plaster...and would still require some metal sequestrant, i suspect...
Not especially cheap, but it seemed to work well for him:
Amazon.com: Purity Pool UAW Underwater Acid Wash Set: Patio, Lawn Garden
(Since the MA worked on it.)
I did mention that the pool was fibreglass and it's in the title
However I will add to my profile
I will wait till I get the test kit before trying Purity Pool UAW Underwater Acid Wash Set.The only thing that bothers me about it is that the black staining is widespread and how much acid will be in the pool. Unless a load of acid in the pool could cure it anyway and then neutralise after.
Opinions please
However I will add to my profile
I will wait till I get the test kit before trying Purity Pool UAW Underwater Acid Wash Set.The only thing that bothers me about it is that the black staining is widespread and how much acid will be in the pool. Unless a load of acid in the pool could cure it anyway and then neutralise after.
Opinions please
Last edited:
Oops, doh, sorry re fiberglass...sometimes when i come back to a post the second time I don't notice the title.
I'm not especially familiar with fiberglass care but in general, you would likely want to stop after using a certain amount of MA via the siphon and rebalance your ph before continuing. Eg. Depending on PoolMath calculations, if you know that half a gallon will drop you x-amount, only use that much in a single session.
Lets see if someone with more FG similarity chimes in.
I'm not especially familiar with fiberglass care but in general, you would likely want to stop after using a certain amount of MA via the siphon and rebalance your ph before continuing. Eg. Depending on PoolMath calculations, if you know that half a gallon will drop you x-amount, only use that much in a single session.
Lets see if someone with more FG similarity chimes in.
- Jun 22, 2014
- 47,783
- Pool Size
- 17888
- Surface
- Fiberglass
- Chlorine
- Salt Water Generator
- SWG Type
- CircuPool RJ-45 Plus
ha ha. I had a feeling you were going to say something like that when you came back.
Also might depend on the age of the FB and if it has calcium carbonate in it. Might be difficult to determine over there, but certainly warrant being extra careful.
That makes sense. Will probably be a big job but if there is light at the end of the tunnel it will be worth it