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Thread: Diamond Brite Onyx - Mottling - Acid Bath - Soda Ash - Milky

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    Join Date
    Jun 2011
    Greenwood, SC

    Diamond Brite Onyx - Mottling - Acid Bath - Soda Ash - Milky

    I have a 24000 gallon IG Diamond Brite Onxy pool that is about a year old. There is a spa and infinity edge with basin connected to it. When we filled it, the PB did a mild acid bath to the spa and catch basin which gave the diamond Brite a consistent uniform finish. The main pool was left alone and we figured that over it would catch up over the next year and the mottling it had would go away over time. After a year I desired more of a uniform appearance to the Diamond Brite Onyx finish. So I talked to the pool builder and he said we could either do an acid wash or an acid bath. The acid wash would require the pool to be emptied and washed as described in many other posts on the web. The acid bath would be a gentler approach where we would shut the pumps off, drop the PH for a day or two, brush the pool until we were happy with the results and then neutralize the acid with soda ash. I elected to do the latter. The PB offered to do it or come and help me do it but it did not look to difficult as I have some science background and have done the TFP method since the beginning and the pool has been crystal clear. He also lives about 90 minutes away, so i proceeded on the my own.
    I added 5 gallons of muriatic acid to the pool, my initial PH was about 7.6, we figured based on the pool calculator, it would bring the PH down to somewhere between 5.5 and 6.0. Mixed it real well and left it alone. The next morning, some of the mottling had come off but not all of it, so I added 2 more gallons of muriatic acid. Using a PVC pipe to direct it to problem areas. The next morning, with a little brushing the pool was perfect, completely black, no mottling. So now to neutralize. I added 10lbs of soda ash, mixed really well and checked PH after 2 hrs, still somewhere bel0w 6.5, pool clear. So I got some more soda ash and found a weblink that calculated how much soda ash was required to neutralize an amount of muriatic acid. Based on the formula, I needed another 25lbs. I added it and the pool turned milky white. After a few hours I backwashed the sand filter and checked the numbers a few times. My last numbers are FCL- 6.97 TCL 6.97 PH 7.3 ALK 148, CH 177. Since my ALK is high I have added acid and am aerating. The milky white is getting better slowly, do i need to have patience or should I add a clarifier? Is the milky white from the alk or the plaster scaling that was removed or precipitate from a chemical reaction.
    24K gal ( pool,spa,basin)
    Pentair Sand Filter, IG Plaster/ Inifinity Edge - Diamond Brite Onyx
    (2) Sta-Rite 2HP, Pentair 400K BTU heater
    Jandy Aquapure SWG w/ AquaLink, Tiger Shark Robot

  2. Back To Top    #2

    Join Date
    Jul 2011
    Arizona & California

    Re: Diamond Brite Onyx - Mottling - Acid Bath - Soda Ash - M

    The milky white is a reaction between the soda ash (sodium carbonate, and a pH of 10.4) added and the calcium in the water, which formed a calcium carbonate precipitate. It would have been better to add mostly sodium bicarbonate and aerating to slowly raise the pH instead of adding only soda ash.

    What you are doing (adding acid to lower TA) is good and just needs some time to clear up. I also suggest adding one lb. of D.E. or Fibreclear to the sand filter which will help clear up the water. Make sure you are brushing everywhere, or else the white precipitate will adhere to the plaster again.

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