GH/magnesium/calcium & KH/potassium

Discussion in 'Aquarium Fert Dosing' started by Henrik, 23 Nov 2008.

  1. Henrik

    Henrik Member

    Messages:
    67
    Location:
    Chester, Cheshire
    Can somebody explain the relationship between GH, Calcium and Magnesium levels? If I know my GH, can I conclude what the ppm levels of Calcium and Magnesium are? My drop test tells me the tap water GH is 4.

    I am using a KH+ product by Sera to boost the KH level (it is 1 in my tap water) - the list of ingredients tells me that it contains Potassium Hydrogene Carbonate and DI ('Aqua Purificate') only. I assume that this will help with my potassium fertilisation as well?

    How do others in very low hardness areas, or those using RO, boost KH? Can I source KHCO3 myself and dilute it to make my own KH booster? Where from? I read in a aquarium water chemistry book that you could also use NaHCO3 for KH boosting, any advantages or disadvantages in this?

    Thanks for any help - I gave up chemistry early in school so my knowledge in this area is a bit poor...
     
  2. ceg4048

    ceg4048 Expert/Global Moderator Staff Member

    Messages:
    8,953
    Location:
    Chicago, USA
    General Hardness (GH) is a measure of the level of Calcium and Magnesium salts in the water. Unfortunately, this measurement does not distinguish between the two so there is no way of knowing what the relative amounts are. JamesC demonstrated some months ago that it was entirely possible to have a high GH reading that consisted of all Calcium salts and no Magnesium. Theoretically the opposite can also occur where the GH is due mostly to Mg and not Ca. These scenarios are unusual but are possible. Therefore having GH 4 could mean either that it is mostly Ca, or mostly Mg or some other combination of both. Many municipal water boards produce reports that give GH "in terms of" calcium carbonate (CaCO3), which for us is meaningless because what this means is that they are saying that the hardness has the same effect "as if" the water had only CaCO3.

    Potassium Hydrogen Carbonate otherwise know as Potassium Bicarbonate (KHCO3) and is used in dry chemical fire extinguishers and is an additive in fizzy drinks.
    If you dose dry salts per EI baseline values then the KNO3 added supply's enough K, but the extra K added by KHCO3 doesn't hurt.

    As it turns out Carbonate Hardness (KH) is a measure of the Carbonate (CO3) and Bicarbonate (HCO3) content. A cheaper alternative is, as you say, to use baking soda Sodium Bicarbonate NaHCO3. But the cheapest option by far is to simply ignore the KH reading because it's not that big of a deal unless you are running a non-CO2 injected tank. There is little to gain by raising the KH. The dreaded "pH crash" doesn't really exist and the plants will not care whether you have KH 1 or KH 5. The fewer adjustments you have to make to your tap water the less tedium and complications you will encounter. I'd suggest to just use the water as is and concentrate on macro dosing and CO2. These have a far greater effect on plant health. You can add a bit of Epsom Salts (MgSO4) to your macro dosing if you want to ensure that there is sufficient Mg. If you are using TPN as your trace mix then it is fairly high in Mg and you needn't worry.


    Cheers,
     
  3. Henrik

    Henrik Member

    Messages:
    67
    Location:
    Chester, Cheshire
    Thanks for the great explanation!

    Admittedly it should not occur on CO2 injected tanks, and since I discovered The Green Machine just 20 minutes from home, I finally have a reliable CO2 refiller and will always keep a filled bottle as a spare... When I originally moved to the UK, however, I really struggled with the CO2 refills, and my tank's ph would run extremely high when the CO2 ran out while the store was again out of stock - given pretty much no buffer capacity at KH 1...

    How does this sound - I get some KHCO3 (still not sure how - any ideas?), and keep the KNO3 dosage a bit on the lower side, as my tap water is at about 15ppm Nitrate already, and I only have about 2W per gallon of lighting. The combination of both should give me enough K. I can then keep KH around 3-4 which would make me feel a bit safer, and avoid having to run at a pretty low ph of 6 or so, which to my understanding would be required at a KH of 1 (I currently regulate to 6.70 on a KH of 4). Any comments much appreciated!

    Do others at a GH of around 4 bother with MgSO4, or do you assume that trace mix and the magnesium element of the hardness give you all you need?

    Thanks in advance for further help - I am pretty close to ordering my salts now (and it's only been five days ago that I first even heard of DIY fertilisers!
     
  4. Ed Seeley

    Ed Seeley Member

    Messages:
    3,262
    Location:
    Nottingham
    injecting CO2 doesn't affect whether a pH crash occurs. Injecting CO2 at 30ppm will lower the pH by around 1 degree, all that differs will be the starting pH which is governed by the other factors that govern pH in the tank. I only inject CO2 during daylight hours so my pH swings back and forth each day with no ill effects.

    When you say 'extremely high' what fo you mean by that?

    You can buy Potassium carbonate from AE but adding the normal levels of EI ferts will give you plenty of K even if you were to drop the nitrate a little. To be honest I wouldn't bother as you could run into problems if your supposed 15ppm Nitrate were to drop without you knowing it as has happened to people on here. Adding a bit too much won't cause anyproblems.

    For the GH I add Kent's RO Right as I use pure RO water and that adds Ca and Mg, among other things. If you're using tap water with a GH of 4 then, unless you're unlucky and have a water supply with no Mg then you shouldn't need to add more separately. The trace does supply some Mg too.
     
  5. Henrik

    Henrik Member

    Messages:
    67
    Location:
    Chester, Cheshire
    Above 8.5. I am amazed that the fish survived - but I had only a few left after the tank was left on its own for a couple of years after two babies within 15 months... Now back on track and already looking quite ok, many new plants and some fish have gone in and are waiting to go...
    My understanding was that if all your Co2 disappears, at low KH, ph goes through the roof. I read this in a book about water chemistry, and they gave a reason...which I cannot remember.
     
  6. Ed Seeley

    Ed Seeley Member

    Messages:
    3,262
    Location:
    Nottingham
    With a low KH your pH should be lower to start with. I'd be investigating why your pH was at 8.5 with no CO2 rather than looking at CO2 to solve that. Bear in mind you never have no CO2 in the water and the only effect CO2 has is to lower the pH. pH should never rise above the usual (non-CO2) tank levels just because you stop injecting CO2.

    The best way, in my opinion, is to completely disregard the effects of CO2 on pH as a factor in keeping fish. A low KH leads to more rapid swings in pH when adding an acid (like those CO2 forms in water) and hence some people believe that you need a KH of 4dKH to be able to inject CO2 safely. My tanks run with 0dKH and I inject CO2 in three tanks with this level. I've never lost a fish due to a 'pH crash' and a lot of the fish are breeding merrily.
     
  7. Henrik

    Henrik Member

    Messages:
    67
    Location:
    Chester, Cheshire
    If it was not the low CO2 at low KH, I cannot tell what made the ph rise. In any case, the tank is now in full swing again and well monitored, ph is at 6.70, KH at 4 and GH at 7 (the latter due to my not realising that the powder hardness booster I was adding would increase GH by more than four times the amount it would increase KH, so I accidentally went up to 13 and am now slowly moving back down with every water change, aiming to land at 5.

    My tap water is 1dKH, but I measure a ph of about 7.5 (in line with the water report I requested from my supplier, which indicates a mean of 7.61)! Is that surprising?

    So what would I have to watch out for if I stayed at my tap water KH of 1? Obviously this would be easier to handle, but I was recommended to go to 4...Would I have to regulate CO2 injection at very low ph levels (around 6?) to obtain the right CO2 concentration?

    Lastly, I just helped set up a tank for a friend (100l) who does not inject CO2, she just uses EasyCarbon. Her KH is equally at 1, and I recommended to add KH booster to it to get it to at least 3. Was that wrong?

    Thanks, Henrik
     
  8. JamesC

    JamesC Member

    Messages:
    1,276
    Location:
    Bexley, Kent
    If you have water with a very low KH and no other buffers present and drive off all the CO2 then the resulting HCO3/CO3 in the water will drive the pH up to about 8.5, so what you said is correct.

    James
     
  9. Henrik

    Henrik Member

    Messages:
    67
    Location:
    Chester, Cheshire
    Just one additional question: I just learnt from my water company that my average calcium levels are 34.4 mg/l and magnesium levels are 5.3 mg/l. I have a book that suggests that 7.14 mg/l of Calcium or 4.3mg/l of Magnesium make up 1dGH. That would make my GH 6, but I only measure 4 with a drop test. Are my calculations right?

    I also have a hardness booster powder made by ROWA which suggests that 1 spoonful per 100l (about 4g) adds a bit more than 1mg/l of Mg and 5mg/l of Ca, but boosts GH by 3dGH (the powder boosts KH by 0.6mg/l). I cannot explain this at all, can anybody help?

    Thansk, Henrik
     
  10. JamesC

    JamesC Member

    Messages:
    1,276
    Location:
    Bexley, Kent
    Water hardness varies during the year so you can't expect to get the same results all the time. Also how does a cheap hobby grade kit compare to how the water board test?

    Other things to think about is how the calcium and magnesium are quoted. Are they in mg/l or Ca2+ or mg/l of CaCO3? 1dGH = 17.86 ppm CaCO3 or 7.14 ppm Ca2+ so it looks like your water board figures are in Ca2+ and Mg2+. But normally GH test kit results are quoted in equivalents of CaCo3.

    A bit more info on water hardness - http://www.thekrib.com/Plants/CO2/hardness-larryfrank.html

    James
     
  11. Henrik

    Henrik Member

    Messages:
    67
    Location:
    Chester, Cheshire
    Can anybody help with this?
     
  12. ceg4048

    ceg4048 Expert/Global Moderator Staff Member

    Messages:
    8,953
    Location:
    Chicago, USA
    If you review post #2 and also post #4 by Ed (who runs low KH tanks) of this thread you'll see that our suggestion is to forget about it. For our intents and purposes the KH of the water has absolutely nothing to do with the amount of CO2 in the water. You still must inject "X" grams per hour into the water column, regardless of the KH, in order to achieve the required CO2 saturation. You seem to be really hung up on pH and KH and what we are trying to communicate to you is that these parameters are mostly irrelevant and that they have no measurable effect whatsoever on plant health or animal health. The KH of the water has no bearing on CO2 injection methods unless, possibly if you are using a pH controller.

    Maximum focus and efforts should be applied to injection stability, flow/distribution, water changes and macronutrient dosing. These are the parameters which will make a significant and obvious difference in the health of the inhabitants of you tank. I can think of only a half dozen or so plants which are actually affected by KH/GH and even so, they will do well outside of their optimal range if these other factors are addressed. While understanding the chemistry issues are definitely important and need to be understood, I can guarantee you that the problems you will face with your tank are not going to be KH/GH/pH related.

    Cheers,
     
  13. Henrik

    Henrik Member

    Messages:
    67
    Location:
    Chester, Cheshire
    I am using a ph Controller so I need to set it to some ph value. I appreciate your point that whatever KH I choose to run at, other factors are more important (which I am all addressing), but unless I am totally mistaken CO2 levels are different with varying ph at a given KH level. If I lower this level, I will need to lower the ph set on my controller...
     
  14. JamesC

    JamesC Member

    Messages:
    1,276
    Location:
    Bexley, Kent
    In theory yes but not in practice. PO4 buffers and others change in concentration over time causing a change in pH but NOT a change in CO2 levels.This is why pH controllers don't work properly within the planted tank enviroment and why all the best aqua scapers in the world don't use them.

    James
     
  15. Henrik

    Henrik Member

    Messages:
    67
    Location:
    Chester, Cheshire
    So how do you control CO2 supply? Do I need to get a tets kit then to check on my CO2 levels, or is there an easier way?
     
  16. JamesC

    JamesC Member

    Messages:
    1,276
    Location:
    Bexley, Kent
    I do it by plant health, drop checker colour and bubble rate.

    James
     

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