black spots in pool...not algea or metals

tara15

Member
Jun 18, 2007
24
My pool has been perfect all year. I went away a month ago and only had someone to bleach the pool a few times, so i bought some HTH algeacide, and the HTH chlorinating tablets. Ever since i've used the algeacide and tablets i've had these black spots on the pool floor. I thought it was algea for a while so was shocking the pool, but they just wouldn't go away. I would vacuum to waste and they would come right back. then one day, while i was vacuuming, i felt the spot and it felt like dirt, very grainy. So I thought it couldn't be algea. I did some reading here and thought mabye I had metals(copper) in the pool. I took the water to the pool store..no I don't have a test kit that tests for metals...and 2 places told me no metals. One place told me that is was probably from the HTH chlorinating tablets if they contained calicum hypochlorite. I checked and they don't, they are trichlor. The algeacide isn't polyquat though...I know i'll never do that again...so not sure if that caused the problem. The guy at the pool store told me to stop using the tabs...thinking they were calcium hypochlorite..and vacuum to waste several time a day, and eventually the spots would go away. I tried that today, and already the spots are coming back. Im getting frustrated and would like to solve this before I close the pool in a few weeks.

So, now after all of my rambling what do you think?

Here are my numbers
FC 5
ph 7.0
alk 40
ca 150
cya 30

Thanks

Tara
 

Darkside of the Pool

LifeTime Supporter
Jul 20, 2010
106
tara15 said:
One place told me that is was probably from the HTH chlorinating tablets if they contained calicum hypochlorite. I checked and they don't, they are trichlor.
tara15 said:
I took the water to the pool store..no I don't have a test kit that tests for metals...and 2 places told me no metals.
tara15 said:
The guy at the pool store told me to stop using the tabs...thinking they were calcium hypochlorite..and vacuum to waste several time a day, and eventually the spots would go away. I tried that today
If they cannot be trusted to at least know there cannot be Hypochlorite tabs, I suggest you do not take their water testing too seriously.

Simple tricks to detect algaes and metals stains:
Gently rub a Trichlor Tab on it. If it goes away it is an algae.
Gently rub a Vitamin C tab on it. If it goes away it is a metal.

Oh, and be aware that some metal removers use phosphonic acid as active element. This raises your phosphate level. This is not relevant, but pool stores often believe otherwise. You'll know where it come from and not to worry.
 

frustratedpoolmom

TFP Expert
LifeTime Supporter
In The Industry
May 20, 2007
12,223
SWSuburban Chicago, IL
From your description it sounds to me like you are getting dust/dirt/pollen or possibly dead algae, settling in spots. Does it poof away if you brush - you mentioned vacuming to waste to it sounds like the dissappear and then return again.

Have you done an overnight loss test? If your FC is holding overnight it's probably not algae (dead or nascent) and I wouldn't worry too much about it - you may have a touch of sparklypoolitis....
 

tara15

Member
Jun 18, 2007
24
No, I havent done an overnight loss test, but when i shocked the pool the other night after i vacuumed, the pool was much better. so, mabye it was dead algea? I thougt dead algea made the pool cloudy.

Thanks
 

thepoolpros.com

In The Industry
Sep 9, 2010
12
coconut creek, florida
The problem, is because you have what they call "copper fallout"
this is because of levels copper ions in the water, eirther by an algacide(yucky), a gas heater, or the source water you are adding.

This problem can be solved by addidng Jacks Magic Blue Stuff. 1 quart per 10,000 gallons.

Keep your alkalinity over 100ppm to prevent this, or dont add any copper to your pool.

What state do you live in ?
 

duraleigh

Admin
Mod Squad
TFP Expert
Platinum Supporter
LifeTime Supporter
In The Industry
Apr 1, 2007
32,154
Sebring, Florida
Most copper staining reported on this forum is not easily removed. What's not clear to me is if OP can easily remove these stains or not. In the first post it does sound like OP is removing the "spots" but they are returning.

So, tara15, are you able to remove these "spots"?
 

tara15

Member
Jun 18, 2007
24
Well, it seems that ever since I've stopped using the HTH chemicals, things are better. I still get spots, but now Im sure they are algea. I just need to get on top of it, but since its getting colder here in NY and I havent swam in weeks, Its hard to get motivated. I will be closing prob this weekend so I'll have to shock before I close. On a seperate note, should I use pollyquat when i close?

Thanks

Tara
 

bk406

Well-known member
Dec 3, 2009
2,690
Central Massachusetts
Check the HTH tabs. Some of them are "4 in 1" or some such thing. HTH tabs with that contain copper. Check the package. My guess is they have copper in them, thats probably where the black spots are from. It could be algea, but my bet is copper from tabs and algecide.