Brown stains spreading

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Firstly if you do not have a pool sweeper with brushes you will need to do a lot of brushing while all this is going on. The fact that your pool is at 72 F is beneficial to the chlorine as it is stronger at lower temperatures.

One reason that you may be getting stains is your REAL alkalinity could be too low for a vinyl pool, if you are not adjusting it, please see below.

You can buy vitamin C POWDER from your local health store DO NOT GET the crystals they will not work as they are non-acidic.

You will need 1 to 1 1/2 lbs per 10,000 gals. Keep the pH low, say 7.0 and sprinkle it around the wall. I did mine at a pH of 6.0 in a gunite pool and it worked very well but a number of persons on this website think that 6.0 is far too low, although ascorbic acid has a pH 6.0; at 7.0 I had limited success.

VERY VERY important drop the chlorine to 0, yes zero, before putting the the vitamin c (ascorbic acid) into the pool, or all the the acid will do is eat up the chlorine and not do the work on the stain. You can buy a chlorine reducing chemical from your local pool store. Sprinkle the powder around the walls or near the stains.

If you are worried about an algae bloom put in one quart of Algaeside 60, not 50, 40 or 30 per 10,000 gals. Then immediately add 3 quarts per 10,000 gals of metal or stain treat (not stain removal) to catch the metal stain in solution.

In regards to the filter adding DE helped catch more particles, then again this may be more in the mind than in reality. With a 300 lb sand filter (9,000 gal pool) add enough DE, through the skimmer box, to raise the pressure by 1, this is about 3 cups, add one cup at a time and wait 15 to 20 minutes. Once you have started the ascorbic acid process you may notice, if you have a sand or small filter, the pressure rising dramatically and your filter slowing down. I back washed for 1 minute only after each of the first two 12 hour periods as the filter became blocked.

It is best to first backwash and then COMPLETELY DRAIN the pool after having run the pump for 48 hours non-stop. If you do not the metal will eventually fall out of solution and cause the stains to reappear via deposit.

Refill and bring the calcium hardness up to at least 200 - 250 for gunite, 100 to 150 for vinyl. I think the higher number works better with stain problems although I am not sure why. Some members have suggested that calcium in the filter helps get the metals deposited in the filter and then washed out in the backwash.

Once you refill it is a good idea to shock your pool first with liquid bleach 20 ppm (Ultra Bleach from Walmart is cheap) at a low pH of 7.2 then after 48 hours bring your pool back into balance and FINALLY add 1 quart per 10,000 gals metal out to keep any metal introduced into pool with the new water in solution. Do this once a month, or as Mbar suggests a little say 3-4oz if the stains reappear.

DO NOT SHOCK if you are not refilling the pool. However if you do not drain and refill you will have the ascorbic acid in solution which will eat the chlorine in large doses. It will take lots and lots of chlorine before you can maintain a stable level. This may take 2-5 days of constantly adding chlorine, a real pain.

If you keep the pH between 7.2 - 7.4 (it keeps the metals in solution) you should not have too many stain problems. Keep the REAL alkalinity between 90 and 100 for gunite, 100 to 120 for vinyl, this also helps keep the metals from falling out of solution, using your CYA number to adjust this. Example a CYA of 70 X ph 7.4 adjustment of .30 gives a reading of 21.0. So your alkalinity should read 120 to get a real alkalinity of 99.0. At a CYA of 40 the adjustment is 40 X .30 or 12.0 so your reading should be around 110 to get a real count of 98.0.

ph CyF adjustment

6.5 0.11
7.0 0.22
7.2 0.26
7.4 0.30
7.6 0.33
7.8 0.35
8.0 0.36
8.5 0.38

If your CYA is 70 then you should keep the Total Chlorine between 7-8. Remember it takes 3-5 days for CYA reading to measure correctly as it dissolves very slowly, so do not add more than is necessary.

Do not shock the pool after you are in balance for at least 2 weeks or it may go cloudy. Add Algaecide 60 if you like.

I learnt most of this from Mbar so you have her to thank.

Finally, two finallys, first if you have blackish looking stain streaks these are normally caused by tannin from leaves, to dissolve these you would need to keep the chlorine up at around 30 ppm for 48 to 72 hours. Carefully monitor your pH level to 7.2 and Your REAL alkalinity to 90-100 for gunite, 100 to 120 for vinyl. Running your pump the entire time. Second, you may still need to do the the muriatic clean process but this is more difficult and should only be used as a last resort, I think doing the ascorbic acid process at a pH of 6.0 is better and less dangerous than putting a muriatic mix of say 1 part acid to 3 or 4 parts water directly onto the wall but once again some members may disagree and I have no experience of vinyl pools.

Aloha and good luck.