brown walls and bottom

[mike518]

I have a concrete with fiberglass walls pool and in the shallow end on one side there is a 18" strip in the middle of the wall that is a light brown as well on the bottom there are light brown sections. Any ideas?

[mbar]

Post a set of your chemistry numbers. It sounds like it may be metal staining. You can tell by crushing up some vitamin C tablets in a sock and rub it on the stain. If the stain lightens, it is a metals stain. Let us know your results.

[mike518]

Hi, I had the water tested at the pool store on Sat. with the following results

FC 2.0
TC 2.0
CC 2.0
PH 7.0
Hardness 180
Alk 100
CYA 60
copper not run
Iron not run

I have brought up the PH ans added about 15 lbs of CAL
Thanks

[mbar]

Hi, welcome to the forum! Your numbers are not too bad, but you can't have a Free Chlorine of 2 and a combined chlorine of 2 & a total chlorine of 2 Your free chlorine added to combined chlorine equals your total chlorine. Anyway you look at it a chlorine level of 2 is not high enough for a cya of 60. Here is a copy of the best guess chart:

Stabilizer . . . . . . Min. FC . . . . Max FC . . . 'Shock' FC
=> 0 ppm . . . . . . . 1 ppm . . . . . 3 ppm . . . . 10 ppm
=> 10 - 20 ppm . . . . 2 ppm . . . . . 5 ppm . . . . 12 ppm
=> 30 - 50 ppm . . . . 3 ppm . . . . . 6 ppm . . . . 15 ppm
=> 60 - 90 ppm . . . . 5 ppm . . . . . 10 ppm . . .. 20 ppm
=> 100 - 200 ppm . . . 8 ppm . . . . . 15 ppm . . .. 25 ppm

As you can see with a cya of 60 your minimum chlorine should be at 5ppms. Your shock level would be 20ppms. If you do have a combined chlorine level of 2 you will need to shock your pool - getting your chlorine level up to 20ppms and keeping it there until it holds within 2ppms overnight.

Did you test to see if the stains are metal or organic? You can do the vitamin C test - or you can also put some ph down in a sock and rub it on the stain. If the stain lightens or disappears it is from metals. If it is from metals then you want to keep the ph low and add sequestering agent before you take your chlorine levels up.

[mike518]

Hi,
I tried the Vitamin C and it did wipe it away. When I rub it with my hand it leave a chaulky white on my fingers and I brushed it and the the water was getting cloudy. I went to the pool store yesterday and the following are the readings
FC 5.6
TC 6.0
CC .4
PH 7.1
Hardness 270
Alkalinity 120
Cyanuric Acid 80
Copper NR
Iron NR
Total solids 895
I add ph+ and the level now seems to be 7.2 I was also told to shock it and the level this AM seems to be really high over the 5.0
Thanks

[PoolDoc]

White residue on your hands could mean any number of things, depending on the underlying surface. Epoxy paint? Vinyl? Plaster? Something else?

Not sure why you were told to shock the pool -- probably because they detected some combined chlorine. Problem is, that wasn't a problem!

If you've kept your chlorine up, and haven't been using an algaecide, the CC they detected could be

• A testing error (VERY common),
• The result of someone having recently whizzed, or sweated a lot, in the pool.,
• The result of using an algecide they told you to use,
• Or something else.

Regardless, CC on outdoor pools go away very nicely by themselves WITHOUT shocking, if you just maintain reasonable chlorine levels. Shock is appropriate if you have extreme CC levels in the spring time, or are trying to get rid of bromide (Yellow Treat, etc.), ammonia (Yellow Out, etc.), algae, or what not.

High chlorine levels from shocking are unlikely to hurt anybody, but could be very hard on swimwear.

Your alkalinity is high enough -- pH+ (soda ash or sodium carbonate) increases carbonate alkalinity. Use borax instead.

Your CYA is high enough. Switch to bleach or calcium hypochlorite instead. Bleach won't increase your alkalinity or calcium, but cal hypo will.

PoolDoc