High CEC with hard water - pointless?

Discussion in 'Substrates' started by ajm83, 20 Oct 2015.

  1. ajm83

    ajm83 Member

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    My water is hard and has lots of calcium in it. Is it therefore pointless trying to use kitty litter or flourite etc to try and retain iron, magnesium and so on for the roots to access?

    My understanding of the chemistry is poor at this point, but if I have understood correctly, then calcium will be exchanged preferentially over magnesium even forgetting the fact that there is a lot more calcium in the first place.

    (Underlying problem is that even as a low tech tank, if I miss dosing for a few days then the plants show deficiencies which I think are either magnesium or iron related. I want to get to the point that the tank can run itself for a while without intervention).

    Thanks
     
  2. roadmaster

    roadmaster Member

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    My water comes out of the tap at pH 7.6 and 12dgh and I use soil mixed with kitty litter and peat with black sand cap for substrate and plant's perform well.
    I also dose 3/4 tsp KNO3,1/2 tsp KH2PO4.1/2 tsp K2SO4 once a week in my low tech 320 litre tank.
    Also add 1/2 tsp CSM+B which has iron,mg, in addition to that from the tap twice a week.
    Have a couple very large sword plant's that are doing well,so I think I must be supplying enough nutrient's including iron, in addition to the nutrient's in substrate.
    Tank mentioned has bee running for a couple year's.
    I sometimes go two week's between water changes, and have skipped dosing for a week without issues.
    Have small tetra's,shrimp's,corydoras,trumpet snail's, and they excrete what they eat back onto the substrate and it is processed by the plant's and used as food.
    I designed substrate to help hold the nutrient's with the cat litter an peat(CEC) and the peat also help's soften the water a bit.
    Many of the root tab's are heavy in iron I believe ,and perhap's these might help with possible iron shortage and epom salt can be used to increase magnesium but I an not familiar enough with sign's of deficiencie's to try and discern what particular nutrient may be lacking ove another,so I add a little bit of all nutrient's as described.
     
  3. ajm83

    ajm83 Member

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    Cheers RM. That's what I was thinking originally, but 1) I have fish that dig, and 2) I tend to uproot plants fairly regularly, so I had ruled out using any kind of soil.

    TBH Even root tabs get on my nerves, often see them little blue and yellow balls popping up out of the substrate and rolling about. :rolleyes:
     
  4. roadmaster

    roadmaster Member

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    Well,If fish you are keeping like to dig,,then they will, regardless of substrates, and keeping stem plant's rooted may be problematic.
    Combine this with uprooting plant's regularly as you say is likely,,,then plant's are gonna struggle.
    Might train my effort's on plant's that can be attached to hardscape (wood/rock) like anubia,java fern's.
    Fast grower's like vallisneria that can do well in hard water and maybe grow fast enough to recover from damage caused by either fishes that dig,and or that nibble plant's.
    Floating water sprite,and or anacharis might also work well.
    used to keep large south American cichlid's that did a fair amount of rooting through the substrate and I placed some plant's like echinodorus,tiger lotus in clay pot's with soil and capped with fine gravel.
    These plant's did much better this way than being knocked around or pulled up by the fish or you/me.
     
  5. ian_m

    ian_m Global Moderator Staff Member

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    I managed to get a few odd plants growing quite well, with "digging" clown loaches by pushing the stem of the plant through a small square of filter floss and burying the floss under the substrate. This stopped them uprooting the plants at least.

    Unfortunately the loaches took to eating the bigger plants, by cutting "U" shaped holes in the leaves.
     
  6. ajm83

    ajm83 Member

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    Thanks, I'm definitely reconsidering soil then.

    But regarding the original CEC/lots-of-calcium-in-my-water :) question, is the answer then that I may as well stick with an inert substrate?
     
  7. ceg4048

    ceg4048 Expert/Global Moderator Staff Member

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    No, you have misunderstood. It may be a problem for some terrestrial plants but aquatic plants really do not care about the relative amounts of Calcium to Magnesium and interference is never really a problem.

    Here is yet another example of a tank with GH 26+ due to extremely high Calcium content. There were never any Magnesium uptake issue-or with any other uptake issues due to high Calcium:
    8395192888_e2cec1da01_c.jpg
     
  8. ajm83

    ajm83 Member

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    Thanks ceg4048, that is a lovely looking tank but I'm not meaning to imply that high calcium is causing a problem with my plants.

    Perhaps I'm asking the wrong question, so please let me try again! :)

    I understand that there are a large but finite number of exchange sites available in the clay. Given that calcium is abundant in the water and also strongly attracted to the surface, would there be a worthwhile amount of other ions 'stored' in the clay or would it simply 'fill' with calcium?

    I mean, the plants are never going to run short of calcium, but they might (and do seem to) run short of other minerals. Therefore If the clay is not going to hold these, but instead be full of calcium ions, it's bringing little benefit.
     
  9. Manuel Arias

    Manuel Arias Member

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    Hi ajm83,

    I think that the comment of ceg4048 is directed to he fact that Ca and Mg exchanges each other in soils, understanding from your original post that you were concerned about the availability of Mg in soil because of this exchange. He is right in that context, and in aquatic plants the proportion Mg/Ca in soil is not critical, as Mg is available anyway in the water column.

    About your questions, you are right when you talk about limited number of positions available for ion exchange. In fact, there are more rules about it. It is not only the number of places but also the type of iones that can be exchanged. For instance, there are three factors ruling here, mainly:

    -The radius (size) of the ions involved in the exchange.
    -The charges of those ions.
    -The electrostatic charge of the surface.

    The exchange happens in two different way:

    -By replacing ions within the crystaline structure of the different minerals.
    -By exchanging ions adsorbed to the surface of the minerals due to the local electrical balance.

    The first one is usually quite independent of the media conditions and related to the stability of the crystaline structures. Because of the crystals have a given entropy, they tend to look for structures with lower level of energy, more stable, which can produce replacement of some ions. However, this is only possible if the ions being exchanged are similar in terms of size and charges. This phenomena, for instance, is the one that controls the exchange of Mg and Ca in dolomite and calcareous rocks, but is quite limited in terms of the exchanges that are allowed, being usually Mg/Ca and Na/K. There are more, of course, but those are the most commons.

    The second one is not really related to the crystaline structure rather than the electrical charge balance of those structures, which generates different densities of negative/positive charges around the surface of the minerals. Some soils like clay, for example, have a lot of surface due to the small size of the crystal compounding the clay, as well as lot of electrostatic charges due to the different minerals composing it. In fact, this electric charges are a big part of the mechanical properties of clay.

    The exchange of ions in the surface of those minerals is much more extensive than the one I mentioned, and it is also controlled by pH at a some point. Low pHs will favour the H+ occupying the negative charge locations, which means that the soil will tend to release elements already attached to the surface of the minerals, like Mg, Na, Ca, Be, Fe, Al, etc. On the other hand, high pHs will favour the negative locations being occupied by the same elements. Of course, when ions are released to the water they are available, but the recovery of the conditions does not mean that the same ions will attach to the same positions, as that depends on the relative concentration of ions in the water vs the ones in the soil.

    In normal conditions, there is always a certain degree of exchanges of cations and anions with the soil, which is depending mainly on the temperature of the soil, pH conditions, as well as the composition of the water column. Temperature favours the exchange of ions, reason why some soils in the past were requiring some heating (not only to favour bacterial activity). pH, as mentioned, has impact in the availability of negative charges in the electrostatic surface of the minerals, and water composition drives what is replaced by what.

    Going back to your question, if your water column is very rich in Ca ions, then it is likely Ca will take over the vacancies in the soil within the time, as the proportion will grant him more chances to get the negative charged locations available in the soil, but the main victim of that will be probably Mg, as is the second most common cations with 2 positive charges.

    However, this is not necessarily negative. The ions need to be released to the water to be available to the roots, so the exchange ion helps to provide them with the elements and molecules they need, as not only cations or simple elements participate of this exchange, as organic compounds like NH4+, NO3-, PO4(3-) also play in this exchange, so a soils rich in some specific elements/molecules acts as fertilizer for the plants.

    Of course, the process depletes the soil after some time, as there are outputs in the system: water changes, trimming of the plants, precipitation of minerals in other forms, etc. This can partly being compensated by adding liquid fertilizers to the water column which helps the deficiencies created in the time for this phenomena in the soil. In fact, the famous ADA step system is thought, precisely, to progressively cover these deficiencies generated in the soil, but relying more in the soil to fertilize the water column.

    I hope this help and/or answer your question.
     
    rebel and Andy D like this.
  10. ajm83

    ajm83 Member

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    Yes, fantastic post! Thank you very much.

    Going to need to read that a few times over to take it all in.

    Andy.
     
    Manuel Arias likes this.

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