Tap and RO pH Problem

Discussion in 'Water Parameters and Additives' started by lIghty, 27 Jun 2010.

  1. lIghty

    lIghty

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    Hi all

    I tested my RO water the other day to find it has a pH of 9.4, this along with a TDS of 25 thought I need to replace my filters.

    I changed my pre-filter about 2 months back so I just got a new membrane from Water Boy. after flushing it I've tested my new RO water to find it now only has a TDS of 2, but it still has a pH of 9.4:whistling: thought this was funny so tested the tap water and it has a TDS of 84 and pH of 9.

    I'm now confused, isn't RO meant to be about 7 or just below? Isn't 9 extremely high for tap water?

    Where to from here as I'm worried that the high pH may damage the new membrane? how do I get it down?

    PS, as I'm using RO though a Kalk stirrer, with a pH of 9 I don't think the kalk is dissolving into the water?
     
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  3. Singularity

    Singularity Hmmm amper!

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    with what are you testing ? Getting a reliable ph reading from RO water is very difficult.
     
  4. LuckyFish

    LuckyFish MASA Contributor

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    Here in Bothasig, Cape Town, the PH of tap water is almost 10, so my RO water is sometimes almost PH 11.
    It is actually not allowed to supply water with such high PH. It is not healthy to use for human consuption.
    The RO unit does not change the PH significantly, especially not from 9 or 10 down to 7 or 8.
    Drinking water has to have a ph between 6,5 and 9,5, otherwise it is not drinking water.
    Dissolve a bit bicarb to drop the ph to the wanted level. That is what I do.
     
    Last edited: 27 Jun 2010
  5. lIghty

    lIghty Thread Starter

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    Henna pH unit, pretty good unit ;)
     
  6. lIghty

    lIghty Thread Starter

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    Well that what I thought, itsn't tap water meant to be 7-8?

    ok, so a bit of bicard will do it then, thats ok as it will buffer it too then, correct?
     
  7. LuckyFish

    LuckyFish MASA Contributor

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    I had to correct my post. Drinking water must have a PH between 6,5 and 9,5.

    You will need extremly little bicarb to buffer RO water as there are no dissolved solids in there.
     
  8. lIghty

    lIghty Thread Starter

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    Would this have any effects on using it though a Kalk stirrer?
     
  9. Singularity

    Singularity Hmmm amper!

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    Anything hand held wont be accurate with RO water, you need some of the best lab grade ph testing equipment.
     
  10. lIghty

    lIghty Thread Starter

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    Its not a handheld;)

    Never the less, the tap is also 9pH
     
  11. lIghty

    lIghty Thread Starter

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    Ok Luckfish, it took a small sample and tested it, the bicard brought it down to only 8.1 before hitting saturation level, how can I get it lower?
     
  12. Reef Maniac

    Reef Maniac MASA Contributor

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    One can not accurately test the pH of RO water - because of the purity of the water, and a lack of buffering capacity in the water, even the slightest contamination by either the container or even the pH probe (if using an electronic meter) could skew the resultant reading quite drastically. You can confirm this by adding just one or two drops of vinegar to the RO water, and testing it again - the reading should then have dropped far more than what the same two drops would cause in normal tap water.

    If the TDS is acceptable (and a TDS of 2 certainly is...) then don't stress about the pH reading.

    I'm sure it is :) Test the post-kalkstirrer, and only start to worry if the pH is then below 12 (saturated lime water should be around 12.3 if I remember correctly :whistling: )

    As an aside, how recently has the pH meter been calibrated, and with what standard buffers? Although it is "normal" to use pH 4.0 and 7.0 buffers, for marine tanks one should be using pH 10.0/10.01 (or 9.0) and 7.0/7.01 buffers, as the instruments do not track linearly from acidic to alkaline...

    You could always use the Borax test to check if your pH probe's calibration is still accurate - I describe this method in this thread: Marine Aquariums of South Africa - View Single Post - Chemical equivalents

    Hennie
     
  13. lIghty

    lIghty Thread Starter

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    Ok, cool :)

    well, it was 25:whistling: so I'm definately happy with 2:)

    I will test as soon as the drump is full! The reason why I thought it was a problem is beacuase my Ca dropped to 300 and I drip every night though a kalk stirrer, but have dosed extra Ca now.

    Funny enough I tested it last night when I found the Ca low and was thinking about it, used the Hanna 7.01 & 10.01 solution, it tested fine.:)
     
  14. lIghty

    lIghty Thread Starter

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    sorry, where my manners, Thanks Singularity, Luckyfish and Hennie! :peroni:
     
  15. Reef Maniac

    Reef Maniac MASA Contributor

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    Ummm, I hope that you are not adding the bicarb to the RO water that you then feed into the kalk stirrer... the sodium bicarbonate will react with the calcium hydroxide (kalk), resulting in insoluble calcium carbonate, which is NOT what you want to add to your tank.

    If you want to increase the calcium capacity of the lime water, rather add a small amount of white vinegar to the RO water, and increase the amount of lime powder you add to the reactor.

    Hennie
     
  16. lIghty

    lIghty Thread Starter

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    No I haven't yet, only done a test, thats why I asked as I wasn't sure. I added a bit of vinigar to the RO last night, as I remembered that it helps the ability for the Kalk to desolve, but how much should I add to say 25L? I added only enough to bring the ph down slightly, was about 50-80ml.....
     
  17. Alan

    Alan Admin MASA Contributor

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    Lighty i have the same problem here in Ballito and as Hennie has said if the TDS is correct at 2 dont worry about the PH. We have had this problem out here for many years.
     
  18. Manic

    Manic Moderator

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    I also tested my RO and tap water and it also has a Ph of around 9. I was hoping this was correct as my calcium reactor would lower the Ph of my tank and the top up water would raise it. Anyways my tank water always sits at a Ph of 8.3
     
  19. lIghty

    lIghty Thread Starter

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    cool, council says their limits are 6.5 - 9.
     
  20. christiaan

    christiaan

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    Hi Guys - sorry I don't meen to hijack here but I too have a Hanna ph handheld and would like to thank hennie for his post here and the link to calibrate the unit!

    I had a question for you guys - My meter states that the probes needs to be soaked in a "storgage soltion" which, of coarse, wasnt supplied. What is the solution or what can I use instead.

    Thanks and again sorry for the hijack.

    Just as a side not - I've had a waterboy RO unit for 2 years now - replaced the prefilters and the resin yesterday for the first time and the TDS reading before replacement was still 0! with a calibrated tds pen! So a big thank you to Marco too!
     
  21. neo

    neo

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    For some other eason I've been reading up on alkalinity and in one artical the following appears:

    "It is easy to believe that water with “alkaline” or basic pH is likely to be high in alkalinity (buffering capacity). However, this is not always true. Water with a high pH but a low alkalinity, albeit uncommon, is possible and regarded as unstable. Aerated RO water (purified by reverse osmosis) or DI water (demineralized by de-ionization) is commonly in this category. Such unbuffered water will quickly decline in pH with the natural accumulation of organic acids in the aquarium. Reef aquarists that are surprised to see a falling or depressed pH in their systems despite high calcium levels may have neglected to measure and maintain alkalinity. "

    so it seems that RO water has a high pH which falls quickly over time, maybe Marco can comment if someone can poke him...
     
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