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Thread: Can use of potash alum/tawas KAl(SO4)2 mess up filter sand?

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    Junior Member sunrise's Avatar
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    Can use of potash alum/tawas KAl(SO4)2 mess up filter sand?

    After using potash alum as a coagulant I have the impression that our sand filter is not as efficient as before anymore. Any experiences with that? Backwashing has been done of course.
    Hayward Pump SP2805X7 Hayward Sandfilter S210T used by switching a manual threewayvalve for either a IG overflowpool with 3700 Gal. or a second IG skimmerpool with 5550 Gal., both tiled with white cement grout and white cement/beachsandrim, the upper pool with sculptured white cement/beachsandwaterfall. Test results: All OK

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    Administrator JasonLion's Avatar
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    Re: Can use of potash alum/tawas KAl(SO4)2 mess up filter sa

    Normally alum will backwash out of the filter without any problems, however in some cases it can combine with other things, like suntan lotion, and form a sticky mess that needs to be manually scraped out of the filter. Instructions for using alum normally specify that you shouldn't run the filter until the alum is removed from the pool, in order to avoid this issue.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Junior Member sunrise's Avatar
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    Re: Can use of potash alum/tawas KAl(SO4)2 mess up filter sa

    Quote Originally Posted by JasonLion
    Normally alum will backwash out of the filter without any problems, however in some cases it can combine with other things, like suntan lotion, and form a sticky mess that needs to be manually scraped out of the filter. Instructions for using alum normally specify that you shouldn't run the filter until the alum is removed from the pool, in order to avoid this issue.
    In the meantime I had the filter apart, removed the sand, checking the tubes and laterals for damages, found nothing, the sand is as it should be up to 6 inch below the top of the filter, no sticky sand found, no accumulations of dirt.
    The situation is as worse as before: Filtering never getīs the fine particles out even after a 6 or 10 hrs. Adding only a handful of alum getīs the water clear after 2 hours.

    Before using the alum the filter worked perfect, however, if the water was cloudy it took sometimes 10 or 12 hrs. to get it clear. Does that mean that now I always have to use alum? It might save electricity, cost here only 0,85 $ per kilo but anyway, I would prefer to go without if if necessary.

    Do I have to change the sand or will thorough washing of the sand (out of the filter since backwashing seems not able to do it) and maybe leaving it in the sun for 2-3 days solve the problem?

    Any experience with that?

    Using the alum to let the fine particles sink down to the floor and then vacuuming it into waste does not work as perfect as catching it in the filter because it will always be stirred up no matter how carefully moving the vacuum.
    Hayward Pump SP2805X7 Hayward Sandfilter S210T used by switching a manual threewayvalve for either a IG overflowpool with 3700 Gal. or a second IG skimmerpool with 5550 Gal., both tiled with white cement grout and white cement/beachsandrim, the upper pool with sculptured white cement/beachsandwaterfall. Test results: All OK

  4. #4
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    Re: Can use of potash alum/tawas KAl(SO4)2 mess up filter sa

    Water clarity begins and ends with correct water chemistry. The filter will only do it's job well if your chemistry is correct. Can you post a complete set of test results?
    Dave S.
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  5. #5
    Junior Member sunrise's Avatar
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    Re: Can use of potash alum/tawas KAl(SO4)2 mess up filter sa

    Sorry, not available because these TFT and Taylor kits are not available in the Philippines, only this:Blue Devil B7770 8-way Pro OTO Test Kit for 30 $, (Same as B7448 w/ Cyanuric, Hardness, Base Demand) see here: http://www.thehottublady.com/liquid-test-kits.html. Do you know this, can you recommend this kit? I would like to measure Cyanuric.
    But the water chemistry was no problem before. Chlorine is kept at 1,5 with Trichloro granular, ph likes to stay at 6,8 and can be raised with soda ash as calculated with the pool calculator to 7.2, making additionally the water cloudy and will be filtered out again??
    Hayward Pump SP2805X7 Hayward Sandfilter S210T used by switching a manual threewayvalve for either a IG overflowpool with 3700 Gal. or a second IG skimmerpool with 5550 Gal., both tiled with white cement grout and white cement/beachsandrim, the upper pool with sculptured white cement/beachsandwaterfall. Test results: All OK

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    Senior Member linen's Avatar
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    Re: Can use of potash alum/tawas KAl(SO4)2 mess up filter sa

    Quote Originally Posted by sunrise
    Blue Devil B7770 8-way Pro OTO Test Kit for 30 $, (Same as B7448 w/ Cyanuric, Hardness, Base Demand) see here: http://www.thehottublady.com/liquid-test-kits.html. Do you know this, can you recommend this kit? I would like to measure Cyanuric.
    No good details on the kit on that webpage, but hopefully the cya test is a liquid one...which is good.

    I am guessing here, but since you are a trichlor user, your cya level is likely high. Many many posters have come on saying just like you:
    Quote Originally Posted by sunrise
    But the water chemistry was no problem before.
    and it turns out the pool finally went over the edge of having too much cya and not enough FC in the pool.
    TFP Moderator who uses Pool School and my TF100 test kit along with PoolMath for my: Round 11K gallon AGP with deep end, 20" sand filter, Matrix 1hp 2spd, 6 2ftX20ft solar panels (and solar cover!), Intex SWCG (copper bars disconnected) and a Rubadub hot tub (chlorine). The SLAM process is not finished until: 1. CC < 0.5 ppm, 2. An OCLT < 1.0 ppm and, 3. The water is crystal clear.

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    Junior Member sunrise's Avatar
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    Re: Can use of potash alum/tawas KAl(SO4)2 mess up filter sa

    Yes I know about that CYA problem and am trying to find out the amounts of test liquid but the "ask a question" button does not work on that website, maybe to keep stupid questions away....

    But before I have that kit, letīs assume that itīs correct, also because we just filled the pool again 3 weeks ago, had a leak, with rainwater btw. How about the behaviour of the soda ash, is that normal to make the water cloudy and will be filtered out again?

    And the sand, can it be messed up by alum?
    Hayward Pump SP2805X7 Hayward Sandfilter S210T used by switching a manual threewayvalve for either a IG overflowpool with 3700 Gal. or a second IG skimmerpool with 5550 Gal., both tiled with white cement grout and white cement/beachsandrim, the upper pool with sculptured white cement/beachsandwaterfall. Test results: All OK

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    Junior Member sunrise's Avatar
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    Re: Can use of potash alum/tawas KAl(SO4)2 mess up filter sa

    Now I got this from my Alum supplier in Manila:

    "Hello Mr. B.,
    Regarding the tawas (local name for alum) used by other clients, mostly have DE filter, and when they use the tawas, their filter elements became brittle. Tawas is quite harsh and it literally eats up materials even marbles, so it could be that the tawas ate up some of the silica sand therefore making the sand irregular in shape, that’s why it is not filtering properly."

    Can somebody here verify that? If that is true, nobody should use it anymore and I have to replace our filter sand.
    Hayward Pump SP2805X7 Hayward Sandfilter S210T used by switching a manual threewayvalve for either a IG overflowpool with 3700 Gal. or a second IG skimmerpool with 5550 Gal., both tiled with white cement grout and white cement/beachsandrim, the upper pool with sculptured white cement/beachsandwaterfall. Test results: All OK

  9. #9
    Mod Squad jblizzle's Avatar
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    Re: Can use of potash alum/tawas KAl(SO4)2 mess up filter sa

    I thought the thing that caught the dirt in the sand was the fact that the grains were "irregular"? Now if somehow this nasty stuff end up smoothing the sand, then that could be a problem.

    If you just replaced all the water, then your CYA may not be very high yet.
    Jason, TFP Moderator
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    Junior Member sunrise's Avatar
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    Re: Can use of potash alum/tawas KAl(SO4)2 mess up filter sa

    That is also what I thought, becoming round instead of irregular. So I will replace the sand and post here if that solved the problem. Before doing that, will test for CYA level with that new kit coming with the sand.

    Any recommendations for a replacment for Alum, another coagulant? If possible several brand names so I can look around here if they carry that.
    Hayward Pump SP2805X7 Hayward Sandfilter S210T used by switching a manual threewayvalve for either a IG overflowpool with 3700 Gal. or a second IG skimmerpool with 5550 Gal., both tiled with white cement grout and white cement/beachsandrim, the upper pool with sculptured white cement/beachsandwaterfall. Test results: All OK

  11. #11
    Mod Squad jblizzle's Avatar
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    Re: Can use of potash alum/tawas KAl(SO4)2 mess up filter sa

    We do not typically recommend or need to use any products like that. Maintaining the chemistry and the use of the filters keep the pools clean.

    Inspect the internals of the filter and verify something is not damaged that could be letting the dirt through.
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
    500 sqft Heliocol solar panels, Dolphin Diagnostic Robotic Cleaner, TF-100 test kit w/ SpeedStir
    Gone: Hayward RS1500 pump, undersized DIY solar heater, Dolphin Dynamic Robotic Cleaner
    Pool School + Test Kit + PoolMath = A TROUBLE FREE POOL
    If you found TFP helpful and we saved you money ... Become a TFP Supporter!

  12. #12
    Junior Member sunrise's Avatar
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    Re: Can use of potash alum/tawas KAl(SO4)2 mess up filter sa

    A few months ago when I had all the sand out I did already inspect all filter and valve parts including the laterals, all OK. Before using the Alum the filter worked perfect so it must have been the use of the Alum. I will post if changing the sand fixed the problem.
    Hayward Pump SP2805X7 Hayward Sandfilter S210T used by switching a manual threewayvalve for either a IG overflowpool with 3700 Gal. or a second IG skimmerpool with 5550 Gal., both tiled with white cement grout and white cement/beachsandrim, the upper pool with sculptured white cement/beachsandwaterfall. Test results: All OK

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