Which filter can reduce KH?

Discussion in 'Water Chemistry' started by Hanuman, 21 Nov 2019.

  1. Hanuman

    Hanuman Member

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    Hello all,

    I would like to know if there is a filter (other than a complete RO system) that can reduce the KH for the purpose of using the water in a tank? I want to acquire some sensitive plants that require a KH<3 and want a way to reduce KH permanently.

    Perhaps Ion exchange filters? Cation exchange? I know those don’t remove the minerals per say and rather swap them but are they suitable/effective for reducing KH? Yes? No? Why?

    Thank you everyone for enlightening me.
     
    Last edited: 21 Nov 2019
  2. Thumper

    Thumper Member

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    Hello,

    cation exchange isn't suitable for in tank use due to the raising CO2 levels which have to gas off. You could go with some acids to remove the KH, but this requires exact knowledge of your KH and how much you would want to remove - and then again different reactions cause difference parameters to raise.
     
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  3. dw1305

    dw1305 Expert

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    Hi all,
    Not easily. Small volumes of water you can boil (carbonate content is dependent on the level of dissolved CO2), but then you need to strain the boiled water through a fine membrane (coffee filter) to remove the precipitated CaCO3. As the water cools CO2 from the atmosphere will diffuse back in and the dissolved CaCO3 will go back into solution as Ca++ and 2HCO3- ions.
    It would need to be anion exchange resin to reduce dKH. You can get them for tap water filters etc.
    You can add an acid, that converts the HCO3- ions to CO2, and the CO2 will then outgas. As you know I'm not keen on messing about with strong acids. Seachem sell an acid "buffer", this is just a mixture of acids.

    It is much easier to start with a low dKH water source, is rain-water an option?

    cheers Darrel
     
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  4. Hanuman

    Hanuman Member

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    Thanks Darrel.

    This would be the best bet then. But isn't sodium exchanged in the process?

    Yes I rather not go down the acid route as it complicate things.

    I would never put rain water in my tank here in Thailand/Bangkok. That water comes with all sorts of nasty things once it washes the overly polluted air. Plus it's the dry season now so no. I simply wanted to know a simple and effective way to drop dKH straight from tap water without loosing too much pressure. I do have an RO filter but it's mostly used for drinking and my smaller tank where I use a 50% tap - 50% RO. That brings dKH to ~3 which is fine. For my bigger tank I don't see myself pouring 50L of RO water in it every week. It's already a pain to change water with buckets.
     
    Last edited: 21 Nov 2019
  5. MJQMJQ

    MJQMJQ Member

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    Chemical filters might work or media eg activated charcoal.Will need replacement every few months and Im not sure how much it can remove.
     
  6. Thumper

    Thumper Member

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    Nope, thats not gonna work.
     
  7. Hanuman

    Hanuman Member

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    As mentioned above, I am not into adding acids to my tank water. I am looking for a filter. As for activated carbon, it will not drop dKH as far as I am aware.
     
  8. MJQMJQ

    MJQMJQ Member

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    Actually ure right haha even if the substances that increase KH are captured by the charcoal they still can react. Buying distilled water may work meanwhile but evaporation is stupid.Tank covers will reduce evaporation.
     
  9. ian_m

    ian_m Global Moderator Staff Member

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    You can use ion exchange resins to swap out the calcium and magnesium for potassium. Just use a standard ion exchange water softener or you can get ion exchange resin in "pillows" for aquatic use and recharge using potassium chloride rather than standard salt/sodium chloride. The potassium carbonate in the water, instead of calcium/magnesium carbonate also acts as a plant fertiliser as well.

    Only issue is potassium chloride to recharge the resin is not cheap, compared to sodium chloride.
     
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  10. Hanuman

    Hanuman Member

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    I will see if I can find some anion exchange filter. What are those "pillows" you are talking about?
     
  11. ian_m

    ian_m Global Moderator Staff Member

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  12. Hanuman

    Hanuman Member

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  13. dw1305

    dw1305 Expert

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    Hi all,
    Like @ian_m says it depends on the resin. The sodium issue is when you use <"strong acid cation exchange"> with Na+ and Cl- as the initial ions.
    Because this is cation exchange, it doesn't reduce the dKH (HCO3- is an anion) but it does reduce dGH (2K+ ions replace one Ca++ ion). Have a look at the Lenntech page on <"ion exchange">, it is a very useful guide.

    This is a description of the process of removing the <"carbonate hardness"> using an anion exchange resin, and a slightly <"more in depth one">.

    cheers Darrel
     
    Last edited: 21 Nov 2019
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