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Thread: Can i scrape these spots off?

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    Can i scrape these spots off?

    Sorry for the poor picture quality, took the pic zoomed in while the sun was getting low. But one day I noticed a significant amount of spots on the bottom of my plaster pool. Seemed like they appeared out of nowhere - I have a weekly pool service so chemistry should be in check according to my testing.

    When I literally touch the spots with my feet, they are raised and hard, seems like it is not so much a stain but literally something hardened on the floor.

    So my question is, is there any harm in me putting some goggles on and going down there with some sort of putty knife and attempting to scrap the spots off? And if I choose this route anything I should do in preparation?
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    Mod Squad zea3's Avatar
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    Re: Can i scrape these spots off?

    Before you try scraping some off lets see if we can identify what is causing it. Could you post a current, complete set of test results? We need the actual number values and not just "ok" or "in range" to give us a starting point at troubleshooting your pool. Also if you could tell us a little more about your pool, such as how old the pool is, if it has been re-surfaced, or if it has been painted that would be helpful too. Are the spots only on the floor of the pool?
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    Re: Can i scrape these spots off?

    Sorry if I'm a little new to this...I dont think I have the complete test results you are looking for but I just used what I have (test strips) to read:

    Free chlorine ~5 ppm
    ph ~7.8 or 8
    alkalinity ~180 pm

    pool was built in 1999, I purchased the house last year so can only comment on its status since then. I don't believe it has been resurfaced as there are some whitish faded areas (not many but still visible).

    I have a hayward sand filter, and have used a krauler sandshark since I have had ownership of the pool - so I have avoided letting leaves, etc. sit on the bottom of the pool.

    spots are only on the bottom of the pool and areas with a slight slope. they aren't on any steeps slopes or steps.

    they seemed to appear around the time my pool company replaced my 2 bottom floor drains, but that seemed to be a manual screw them in type job so I don't know how anything could have spilled, etc.

    thanks for the help! sorry if my initial post was less than informative.

    edit - further details - water quality is good and has always been since I had the pool. also pool is located in the phoenix area

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    Mod Squad zea3's Avatar
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    Re: Can i scrape these spots off?

    Test strips don't give very reliable results, but I understand it is all you have for now. It is best if you have a high quality, FAS-DPD based test kit, such as a TF 100 or a Taylor K2006. For now if you could take a sample to a pool store and have the water tested for FC, CC, TA, pH, CYA, and CH, then post the results here that would be helpful. If your test strip result is accurate, your pH and TA are both high. If you CH (calcium) is also high that could be the root of your problem.
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    Re: Can i scrape these spots off?

    Have you tried just brushing the pool? Does that seem to help?

    What type pool brush are you using? SS/wire, nylon, combo ?

    The best thing you can do for your pool is get one of the recommended test kits.
    This is what will put you in control of your pool. Here's a link on test kit comparisons: pool-school/pool_test_kit_comparison
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    1)You lose 1ppm or less FC overnight, & 2)You have .5ppm CC's or less, & 3)your water is clear.

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    Re: Can i scrape these spots off?

    I use a nylon brush that seems pretty worn. Would a good wire brush be a good start?

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    Re: Can i scrape these spots off?

    Raised spots that are hard are most likely "calcium nodules." They turn dark when dirt and metals stick to it due to its porosity. Generally, the cause of these spots is due to delamination (or bond failure) of the plaster from the underlying substrate, whether it is gunite or old plaster. If the pool company drained your pool to install the floor drains, that would allow the plaster to shrink or expand and then loosen its bond. It is also very likely that the pool has been replastered before, because it is usually very difficult to get a good and effective bond onto old plaster, but it doesn't have to be from that. If the original plastering wasn't done correctly, then it could simply be delaminating from the original substrate or gunite. Also, if the plaster has severe cracking, nodules will also form on those cracks.

    The forming of calcium nodules is a unique and isolated chemical reaction between the water and newly exposed pool plaster. It is difficult to explain, but the important thing to understand is that it is not due to improper or unbalanced water chemistry. In fact, balanced pool water is what facilitates this formation.

    Sanding the calcium nodules with 80-100 grit (wet & dry) sandpaper is probably the best way to remove them, but yes, a putty knife will work to, but also scapes areas around the nodules and leaves marks in the plaster. I doubt a wire brush will work effectively in removing them. If you drain the pool, that will only compound the problem and more nodules will develop after you fill the pool again.

    Here is a link that explains how nodules are formed. http://www.poolhelp.com/handouts/oB_Cal ... andout.pdf

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    Re: Can i scrape these spots off?

    I forgot to mention that calcium nodules, unfortunately, usually continue to form again even after removing them by scaping or sanding. That is one of the frustraing things about them. In some cases, nodules do not form again. There is no way of knowing for sure until you remove them.

    You might want to check with the previous owners to determine whether or not the pool has been replastered recently. If it was within a couple of years, it might be still under warranty. The lack of proper bonding is a workmanship issue. If the plastering hasn't been redone since 1999 as you mentioned, then the warranty period has expired. Sorry for the unfortunate and disappointing information.

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