# extremely low kh in local tapwater



## mike b (25 Feb 2015)

Hi there. My tap water kh is virtually zero. Up to now I've been using liquid carbon but I want to go onto a pressurised cylinder. Now I know that kh has to be at least 4 to avoid ph drops but I wondered what's the best way to buffer my tapwater?Remember I do 50% water changes a week in accordance with ei. Is it best to use a kh buffer or maybe mix some coral gravel into my aquarium gravel. If anyone has low kh tapwater like me please can you give me some advice on the best way to get my kh up to at least 4?


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## ian_m (25 Feb 2015)

http://www.aquaessentials.co.uk/seachem-equilibrium-600g-p-98.html
http://www.aquaessentials.co.uk/tropic-marin-remineral-tropic-200g-p-3704.html

Or roll your own...
http://www.theplantedtank.co.uk/RO.htm


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## dw1305 (25 Feb 2015)

Hi all, 
You can have water with any dKH value <"Wanted: pictures of tanks ........">, it is only in the drop checker that you need to know the solution is 4dKH solution <"CO2 measurement using a drop checker">.  

In really soft water it is impossible to obtain pH stability. Have a look at <"What is worse: permanently high CO2 or dramatic pH swing?">

If you want to raise your dKH you can use an aragonite source of carbonate (Oyster Shell Chick Grit is the cheapest option and more environmentally friendly than coral gravel)  or you can use potassium bicarbonate (KHCO3), which is soluble. 

Using potassium bicarbonate - 1.8g KHCO3 in 25 litres of water = 2 dKH, (from <"James' Planted Tank - Remineralising Agent for RO Water">.

cheers Darrel


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## mike b (25 Feb 2015)

Ok so say I use oyster shell in my tank to raise the kh to 4 (I know it can be higher but I will use 4 as an example) and I do a 50% water change with my tapwater that has a kh of approx 1 (I'm being generous saying 1. It is that low) would that kill off my livestock? I know oyster shell is slow acting and doing a 10% change wouldn't make any difference but a 50% would?


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## mike b (25 Feb 2015)

Better to treat the tapwater before it goes in my tank but I would imagine it would take a while for oyster shell to buffer the kh up.


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## Chris Jackson (26 Feb 2015)

hi, well i'm in Cornwall with extremely low KH that measures nil with a test kit. I simply add bicarbonate of soda from a supermarket to get a KH of 5. Have done it for years with no problems and you soon get to used to getting the dose right.


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## Edvet (26 Feb 2015)

Be glad, it's far easier and cheaper to get KH up than down


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## mike b (26 Feb 2015)

I used to use bicarbonate of soda years ago when I was keeping discus. Do you find that the kh drops during the week? I found bicarb to have a temporary effect on kh and ph.


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## Chris Jackson (26 Feb 2015)

Oh really, no, I've not found that at all. I'm on 50% changes weekly and the tank holds pretty steady in the 4-5 range.


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## dw1305 (26 Feb 2015)

Hi all,





mike b said:


> Ok so say I use oyster shell in my tank to raise the kh to 4 (I know it can be higher but I will use 4 as an example) and I do a 50% water change with my tapwater that has a kh of approx 1 (I'm being generous saying 1. It is that low) would that kill off my livestock? I know oyster shell is slow acting and doing a 10% change wouldn't make any difference but a 50% would?


No, it should be fine, you will still get relatively slow changes  in  water chemistry. HCO3- is a "weak base", and in equilibrium with CO2 (as H2CO3-) a weak acid, so this is a "buffered system". 





Chris Jackson said:


> I simply add bicarbonate of soda from a supermarket to get a KH of 5. Have done it for years with no problems and you soon get to used to getting the dose right.


 Sodium bicarbonate (NaHCO3) works just as well to raise dKH. The only reason for preferring potassium bicarbonate (KHCO3) is that the potassium ion (K+) will be taken up by the plants, whilst the sodium ion (Na+) won't. This is why the sea is salty with 99% NaCl, plants don't have much requirement for either Na+ or Cl- ion so they have a very long residence time in the sea water. 





mike b said:


> I used to use bicarbonate of soda years ago when I was keeping discus. Do you find that the kh drops during the week? I found bicarb to have a temporary effect on kh and ph.


 You can exhaust the HCO3- ions, it is because NaHCO3 full disassociates, so you have no reserve of ions (the system isn't "buffered").

This isn't as relevant for planted tank keepers, and if you are changing 50% of the water every week, its just not going to happen.  There is an explanation at the excellent <"Skeptical aquarist - Bio-acidification">.

That is also one advantage of the coral gravel/shell grit approach, you have a reserve ("buffer") of  "insoluble" CaCO3.

Hope that makes sense.

If you are using EI you can just add KHCO3 with the rest of your salts. 3.6g KHCO3 in 25 litres is 4dKH.

cheers Darrel


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## Chris Jackson (26 Feb 2015)

Thanks Darrel, very intersting.


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## mike b (26 Feb 2015)

Excellent explanation Darrell.  Really interesting. Seeing I'm dosing ei anyway it seems that potassium carbonate might be the way to go. You say 3.6 gram per 25 litres of water. I know everything ei is estimated but what would 3.6 grams equate to? Half a teaspoon, a teaspoon more? Sorry I'm not up on grams.


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## dw1305 (26 Feb 2015)

Hi all,





mike b said:


> You say 3.6 gram per 25 litres of water. I know everything ei is estimated but what would 3.6 grams equate to? Half a teaspoon, a teaspoon more? Sorry I'm not up on grams.


 A tea spoon is ~6 grams.

cheers Darrel


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## ian_m (26 Feb 2015)

Generally 1tsp is about 5-6gr.


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## mike b (26 Feb 2015)

Thanks. Great advice.


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