Discussion in 'Water Chemistry' started by JamesC, 16 Feb 2009.
They steal all your gold and then lose it over a cliff in Italy?
Welcome to the Internet!
Pity you aren't allowed to link to other forums on TFF...
lol, i always slip the occasional sneaky link to UKAPS
How come only the ions of calcium and magnesium carbonate are used in measuring KH?
Because when we talk about water hardness it is always related to calcium and mangnesium ions. As carbonate hardness is a measurement of a part of water hardness it must relate only to Ca++ and Mg++. It is confusing and many people get it wrong, even Wikipedia's entry for carbonate hardness is incorrect. Doing a quick search on Google showed that most websites (mainly aquarium) have the definition wrong with just a handful having the correct definition. Aquarium KH test kits are really alkalinty test kits and this is the main reason for all the confusion IMHO.
I have done a bit of reading since you started this thread, with the same findings as you James. I had my doubts, though, as a lot of them did mention adding CO2 would reduce KH too.
Another demerit for hobby test kits, I think.
EDIT:I actually used to know a lot of this stuff when I first started in the power industry, where water chemistry is vital. Unfortunately, I have forgotten a lot of it and have been too lazy to relearn it. Now you have saved me the trouble.
I used to get it wrong as well up until recently as I thought adding CO2 would increase KH. When CO2 is added to water carbonates are formed so I naturally thought that as the carbonate content had increased then the KH had increased.
It's quite easy to tell if you have a KH test kit or an alkalinty one. If you add drops from a single bottle until the solution changes colour then you have an alkalinity test kit. If you have a test kit like this - VISOCOLORÂ® ECO Carbonate hardness - with more than one bottle then you most likely have a proper KH kit.
i have a full blown uKaps sig and so far have not been caught by the 'forum police'
Just noticed there is another thread on the subject o links in other forums just started in off topic so maybe we should post there about this now
Really interesting article. Following general advice to keep KH up above 4 dKH, I use Nutrafin pH Stabiliser to boost KH a little as it tends to drift to almost zero. This seems to help keep pH pretty stable. I assume (unless anyone knows better) that the product is basically a (very expensive) solution of sodium bicarbonate. Adding 10ml to each 70L of tank water raises KH by 1 degree.
I was thinking of making up my own solution and wondered if anyone else did this and, if so, what strength sodium bicarb they make up. I see the argument above that it doesn't matter if KH is zero but I feel happier with some small level of KH buffering. Would welcome any comments or advice on this.
I've just run my tank with a zero KH for a couple of weeks and though all my tetras loved it my cory's were not happy. I'm now in the process of slowly raising it back up to 1 KH which is were I like to keep it.
Your pH stabiliser could well just be sodium bicarb so to save money you could make your own. Even better than sodium bicarbonate is potassium bicarbonate, or if you can't get that, potassium carbonate which is available from some of our sponsors. Some plants don't like sodium which is why the potassium compounds are better.
These are the dry amounts you need to use:
Sodium bicarbonate - 1.5g in 25 litres of water = 2 dKH
Potassium bicarbonate - 1.8g in 25 litres of water = 2 dKH
Potassium carbonate - 1.2g in 25 litres of water = 2 dKH
Thanks James for that helpful response. On a re-reading of your original article I see that what I'm really boosting with sodium or potassium bicarbonate is alkalinity and that strictly speaking I would have to use Magnesium or Calcium bicarbonate to boost KH proper. Forgive my ignorance but all this raises more questions in my mind:
1. What is the practical difference between boosting alkalinity and boosting genuine KH? I assume both will help buffer pH
2. I see that I can more easily obtain potassium carbonate than potassium bicarbonate. At appropriate doses as you set out, do both do the same job? I'm wondering if some of the carbonate will become bicarbonate in the aquarium by reacting with acid - sorry my chemistry is not up to knowing this!
3. If I could use potassium carbonate instead of potassium bicarbonate, could I use calcium carbonate rather than calcium bicarbonate? Aren't limestone and coral sand largely calcuim carbonate? Could this slowly boost KH?
Any further comments will be gratefully received and I'm sorry to throw yet more questions at you. Your responses are excellent so you've only yourself to blame!
Yes, using sodium or potassium bicarbonate increases alkalinity and not KH as sodium and potassium are not multivalent ions, ie they only have a single + rather than for example calcium that has ++
None really for our purposes.
The amounts that I give will adjust the alkalinity the same. KH is defined in parts of CaCO3. Carbonates are different to bicarbonates and this is where people often go wrong doing the calculations. One carbonate will dissolve in water to give two bicarbonates so this has to be taken into account if sodium or potassium bicarbonate is used. Another way of looking at it is that each CO3-- can neutralise 2 hydrogen ions (acid) and HCO3- can neutralise only 1 hydrogen ion. The process of dissolving carbonate in water actual removes CO2 to form the bicarbonate. This results in a large rise in pH so if you do choose to use carbonates to adjust alkalinity then you have to take extra care and do it slowly. This is why using bicarbonates is safer.
Yes you could use calcium carbonate but it's pretty insoluble. KH is defined in parts CaCO3. Problem with using crushed coral, etc is that you don't know at what rate the CaCO3 is going to dissole. Some people do use it though but takes some trial and error to get right. Also raises GH.
No problems and thank you for your interest.
James, thank you so much for a brilliant reply. Has really helped my understanding.
Would it be fair to say that total hardness is the same as total dissolved solids (TDS)?
Nope, TDS is something else. Water hardness is only concerned with multivalent cations, ie. Ca++, Mg++, Al+++, Fe+++. If you add say some table salt (Na+Cl-) then this doesn't affect the hardness but does raise TDS. Water hardness does contribute to TDS but not all TDS is necessarily water hardness.
I have some beautiful limestone rocks that I bought ages ago and have been sitting in my garden as the large mbuna tank I was going to use them for was veto'ed by the wife! I would like to use them in a planted tank with a dark substrate, but am worried they will affect the hardness of the water too much. How would it affect the plants, red crystal and amano shrimp I would like to tranfer to the finished tank?
Personally I wouldn't add it as you have no idea to how fast or slow it is going to dissolve and affect the water's parameters. Some people do add it so it isn't a big no no, you just have to be aware of what is happening in that it will raise both KH and GH.
Have decided against the limestone following your advice, I have some other rocks from my LFS, which won't contrast as nicely with my planned dark substrate, but should still look pretty good. Saw George at the Festival of Fishkeeping doing a trial tank hardscape with some dark substrate at the APS stand and he was using some beautiful rocks, which have better strata than the ones I will be using but were a similar colour. Hopefully will look great anyway, have just ordered the plants from The Green Machine so looking forward to starting the scape in the next few days. Will post some pictures once in it is ready.
Hi James, great write up!
I have been struggling to try and find an ideal GH range which would suit most plants. I live in Malta and most of our water is obtained from the Mediterranean Sea via huge revers osmosis plants. Since I live close to one of these plants, my tap water has a low KH reading of 3 (according to the liquid tests that is) and a GH reading of 6.
Would you say that the GH reading is fine for most aquarium plants or would you rather see a higher of lower GH value?
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