light brown-tan stain on the walls-floor of my pool....ugh

[kennyb30]

hey guys, bought a house 3 weeks ago that had a pool, 20x 40 inground gunite, the water looks great, but now im getting this stain on the wall all of the sudden. its hard to notice it unless u get in the pool, then with goggles on you can see it easily, im starting the BBB method after 2 weeks of using the pucks, got a TF-100 test kit in yesterday and it looks like everything is ok, except Ph might be a little high. any idea to what is causing this light brown-tan stain i'm seeing. thanks guys! (awesome forum btw)

TH 400
FC 5
PH 7.8-8.0
TA 120
CYA 50

 

[JamesW]

Re: light brown-tan stain on the walls-floor of my pool....u

Most likely calcium carbonate scale and/or iron. Lower the pH to 7.2 using muriatic acid until the TA gets down to about 70 ppm*, and then keep the pH at about 7.4 until the scale and/or iron is gone and then keep the pH at about 7.5. Brush frequently to help remove the scale and/or iron. Check out the pool calculator and pool school for more information.

http://www.poolcalculator.com/

pool-school/

Also, you're reporting TH as 400 ppm; I am assuming that that is Total Hardness. Total Hardness is not as important as Calcium Hardness. If you can double check to find out the Calcium Hardness and iron levels, then that would be helpful. What is the water temperature?

Adding a sequestrant would also be helpful. You can try using ascorbic acid (Vitamin C) to see if it will remove the stain. If it does, then the stain is most likely iron.

pool-school/metal%20stains

*[edit] This is assuming that the calcium level is high and that you're using bleach. If the calcium is not high or you're using tabs, then you don't want to lower the TA to 70 ppm. With a cyanuric acid level of 50 ppm, you should not be using many tabs anyway (if you are still using some tabs).[end edit]

 

[kennyb30]

Re: light brown-tan stain on the walls-floor of my pool....u

will try to get the PH down this evening using muriatic acid, i haven't checked the calcium hardness yet with the test kit, i will do that this evening also, what sequestrant do you recommend James ?

 

[JamesW]

Re: light brown-tan stain on the walls-floor of my pool....u

ProTeam's Metal Magic and Jack's Magic the Pink Stuff (regular), the Blue Stuff (fresh plaster), and the Purple Stuff (SWG) are some of the top sequestrants. You can also find many other brands with similar products, some of which are noticeably less expensive. Sequestrants based on HEDP, phosphonic acid, or phosphonic acid derivatives are the most effective.
pool-school/metal%20stains

Note: White, off-white or tan stains/deposits are usually calcium carbonate. Brown or orange/brown stains are usually iron.