Brown/yellow spots accumulating on plaster

[DonaldVS]

Hello,

Newbie to Pool Forum seeking guidance. I have some iron stains left from nails that were on bottom of pool for 2+ years while pool was closed during home construction project. I saw on forum that vitamin C tablets / ascorbic acid may remove the stains. After rubbing the equivalent of 8 to 10 tablets on stains I saw little change to the dark brown stains perfectly shaped like nails. However, a couple of days later I found brown/yellow powder gathering on the bottom and sides of pool. When I brush the powder that is accumulated in spots bottom and sides of plaster-- the powder dissipates into the pool water and the surface appears clean. The next day the brown spots reappear, and I once again brush off. I have a Hayward DE filter on my 25K gal gunite pool that runs 12 hours per day, but I do not believe that it can filter out this "powder" like substance. I believe the substance is vitamin C residual because I never saw the powder or had problem before trying the Vitamin C, and the Vitamin C tablets are the same orange/brown color as the stains.

Thanks for any thoughts/ help.


FC 2.5
cc 0
TC 2.5
alk 100
cal 140
cya 30
ph 7.2
temp 84 with full sun for 8 hours

25k gal. gunite, with hayward DE filter, 72gals/min, 1hp motor, pump runs 12 hours per day, have been using Chlorine pucks, but starting want to practice BBB

[mbar]

Hi, welcome to the forum! I don't know what the brown powder is for sure, but I do know that I have used Ascorbic Acid (vitamin C) and it is very soluable in water. I would recommend you use a Mr. Clean magic eraser on the rust stains from the nails, or a very fine sandpaper. Rust stains don't seem to go away with vitamin C. My suggestion would be to take your chlorine up to shock level, or at least to the high point of your cya chlorine demand, which at cya of 30, would be 6ppms. The high chlorine level should break down whatever the powder is. Here is a chart that shows what the best levels of chlorine are to the amount of cya you have in the water.

Use the info in this chart to help you figure out what levels of chlorine you need to maintain in your pool based on the amount of CYA (cyanuric acid, also called stabilizer) that you have in your pool. (FC = free chlorine)

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 you would need to take your chlorine up to 15ppms to reach shock for your water. The high chlorine levels will also help to lighten the rust stain. Feel free to ask any other questions you may have.