# low KH problem or not?



## Ady34 (26 Aug 2011)

Hi all,
this is my first post after recently joining the ukaps forum. I joined as im in the process of setting up my first real attempt at a planted aquascape and was looking for good advice!
I have confused myself about KH and its importance, and although i know it helps keep a stable ph, have found much information stating it is also necessary in maintaining healthy bacterial growth in filters and trace elements vital for plant growth. However, i have used ada aquasoil amazonia as my substrate (along with powersand special m and penac p) and in the ADA publications it states that aquasoil amazonia reduces not only the ph, but lowers kh to less than 1dkh, which i thought to bee too low - ph crashes etc. My tap water has a kh of less than 2dkh anyway and ive always struggled with increasing it without increasing my ph too much also (tap water ph 7-7.5). I will be adding pressurised c02 also and am worried about ph crashes. Do i need to worry as much as im becoming a little obsessed! Basically i have 3 questions:
1. should i increse my kh while cycling the tank to ensure proper bacterial colonisation?
2. should i continue to buffer my kh long term to ensure a healthy running tank or will regular weekly 45% water changes ensure a stable ph and provide whatever else the filter bacteria need (except fish wastes etc)?
3. what role, if any, other than ph stability does kh play?
The scape will be planted with mainly crypts, hairgrass, moss, ferns, pogostemon halferi and hygrophilia pinitafida. Ill be fertilising with tpn and tpn+ further down the line if necessary.
Any sound ( and not too confusing) advice will be much appreciated.
Thanks
Adrian.


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## Radik (26 Aug 2011)

PH crash is myth. I have tank with low KH (2-3) deliberately for soft water fish where I often overdose Co2 my PH ranges from 5 to 7 during the day/night as I inject Co2 and every fish is swimming happily. For shrimps this can be issue but for fish no problem. You can't lover PH more than 5 with CO2 anyway and given lower KH you can try difficult plants like Toninas or Eriocaulons. KH hovever play no role for majoriry aquatic plants.


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## viktorlantos (26 Aug 2011)

We do use full RO on our planted tanks. There are no pH swings however with frequent water changes (daily for example) at the cycling you can have that. Let's say the RO produce a lower pH water and your Aqua Soil Malaya with CO2 keeps that low. We had an issue with it one time but not since then as we do the weekly changes.

The bacterial growth as i know will slow down with low pH. So that maybe something what you need to watch at cycling. But otherwise i do not see risk if your fishes and shrimps is compatible with these water parameters.


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## hotweldfire (26 Aug 2011)

Darrel said on my journal thread recently that for low KH systems big changes in PH aren't that meaningful. The explanation was just at the edge of my understanding so have a look at my nano journal for it. Or maybe he'll explain here.

RE: KH, there's this thread on PFK at the mo' (just read the last page first):

http://forum.practicalfishkeeping.co.uk/showthread.php?t=77688&page=4

I would also appreciate expert advice on this issue as am worried that the disasters I've had in my tank might be down to low KH. I.e. the tank's not really cycling.


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## viktorlantos (26 Aug 2011)

Yup i also not experienced big pH changes with soft water. And the slower cycling was less noticable. You also can help with that with additional bacterial boosters.


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## Ady34 (26 Aug 2011)

thanks for the responses guys,
wow Radik a 5-7 ph swing, i'd be terrified!
Currently the water is at 6-6.5ph which is fine, but it did drop to 5.5 in the early stages perhaps due to the ammonia spike? I carried out 45% water changes every 3rd day which brought the ph back up. I dont know if its ok to do frequent water changes during cycling, but thought with the ph dropping that low the cycle would have stalled anyway so would be better off doing them!
Im on a bit of a budget so dont want to go down the RO water route, but if its ok to run a planted tank with low kh and c02 then ill stick with my tap water and keep up with water changes.
I wanted to cycle, plant up, add the c02 and then check my perameters and adjust if necessary. However with crypts ive read they can be susceptible to fluctuations in water chemistry, so dont know if id be better off cycling, adding c02 and seeing where i stand before draining and planting? I also want to keep shrimp as part of my algae crew and know that they are susceptible to fluctuations also. Its maintaining the stability im most concerned about and with less than 2 dkh im worried that the c02 addition will drastically reduce my ph. I dont really know about the chemistry involved so i may be putting 2 and 2 together and coming up with 5!
Hotweldfire, ill def look up your journal as that low kh/ph relationship sounds very interesting. Thanks.
Thanks again for the replies they are putting me at ease a little.


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## Radik (27 Aug 2011)

Why terrified? I told you PH crash is myth and more important is water TDS than PH... Fish do not mind PH fluctuation but they would mind high TDS jump in water and that's what usually happens when you change water. When not careful enough your new water TDS is different than original tank water due organic waste or fertilizer etc and so it comes with PH change of course if you inject Co2 but PH fluctuations are fine. In fact when you try to buffer KH with bicarbonate etc then effectively you are changing TDS and then some fish can have problem adapt quickly.

Also no need for daily water changes.. weekly is fine.


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## Ady34 (27 Aug 2011)

Thanks Radik,
is tds total dissolved solids ie gh or kh (total hardness)?
if so, are you saying as long as my water change water measures the same as my tank water, all will be ok?
My tap water has low kh and gh also so i wont have a problem matching the tank and tap water as they are within 1dkh and 1dgh respectively.
Basically i shouldnt worry too much about my low kh as long as my water changes are weekly and of similar perameters.
Thanks again, i feel much happier now.


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## dw1305 (29 Aug 2011)

Hi all,
Hotweldfire wrote: 





> My understanding of this is what a PH kit tests is the proportion of OH- ions to H+ ions, not the amount of OH- or H+ ions there are in the water. In a (_non_)buffered system the ratio can swing massively but the quantity of the ions can remain relative stable. In contrast in buffered (high KH) systems a big PH swing is suggestive of a really massive swing in the quantity of OH- or H+ ions. This is what is going to impact on fish health. Not the relative balance between them.


Thats the jist of it and much better summary than I managed. This is the "balance" image,  pH is the relative position of the two ends, and the TDS is the size of the "weights". If those "weights" are very small (low dKH), a high pH can be drastically lowered by the addition of a small amount of weak acid (like humic acid or carbonic acid from dissolved CO2).






cheers Darrel


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## Radik (29 Aug 2011)

Ady34 said:
			
		

> Thanks Radik,
> is tds total dissolved solids ie gh or kh (total hardness)?
> if so, are you saying as long as my water change water measures the same as my tank water, all will be ok?
> My tap water has low kh and gh also so i wont have a problem matching the tank and tap water as they are within 1dkh and 1dgh respectively.
> ...



TDS is all dissolved things in water GH,KH, fish and plants waste, fertilizer or other minerals. In general if you have lot of livestock or do EI dozing you can measure it after and before water for my fish tank it is around +-10-20TDS change.


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## gmartins (2 Sep 2011)

dw1305 said:
			
		

> Hi all,
> Hotweldfire wrote:
> 
> 
> ...



I understand the idea that you can change TDS without messing up with pH (e.g. proportionally reducing the size of blocks on both the left and right in the figure). However, if pH is the ratio of H+ and OH- I cannot see how it can be kept constant while changing TDS.

GM


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## dw1305 (2 Sep 2011)

Hi all,


> However, if pH is the ratio of H+ and OH- I cannot see how it can be kept constant while changing TDS.


Yes it can, without getting too bogged down in the chemistry, every ion is either an acid (H+) donor or a base (H+ acceptor), but in a lot of cases we can ignore this, and they will have no effect on pH. 

The H+ and OH- ions (really this should hydronium H3O+ and OH- ions  - "_2H2O is in equilibrium with OH- + H3O+ H3O+ and OH-_") are the proxy that we use as pH to measure acidity and alkalinity. Any compound that we add that goes into solution will add TDS, but it will only change the pH, if it changes the relative balance of H+ and OH- ions.

For example for salt, sodium chloride (NaCl) 





> In NaCl solution you have very weak Bronsted-Lowry base (Cl-) and very weak Bronsted-Lowry acid (Na+). They are so weak, you may treat them as simply neutral."


So for all practical purpose you may safely ignore both Na+ being an acid and Cl- being a base. So a salt like NaCl will disassociate into Na+ and Cl- ions, but it won't change the pH. 

You can get this from the pH7 end point of the classic acid base reaction as well -  HCl (aq) + NaOH (aq) ? H2O (l) + NaCl (aq).

cheers Darrel


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## gmartins (2 Sep 2011)

dw1305 said:
			
		

> Hi all,
> 
> 
> > However, if pH is the ratio of H+ and OH- I cannot see how it can be kept constant while changing TDS.
> ...



Ok I see. You change TDS because you are adding salts but since you're not adding any H+ or OH- this does not affect the pH. You add the same proportion of positive and negative ions (Na+ and Cl-) so the balance is maintained.

cheers,

GM


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## dw1305 (3 Sep 2011)

Hi all,


> You add the same proportion of positive and negative ions (Na+ and Cl-) so the balance is maintained.


That is exactly it. Although it sounds a bit strange, even though we have known about acids and alkalis for hundreds of years, the actual chemistry  that  defines why a compound will be an acid or an alkali was only teased out in the 20th century. That is why we use pH, depite its limitations. 

This acid/base equilibrium is how "pH buffers" work, an example would be the carbonate/CO2 equlibrium we use for drop checkers or the phosphate buffers (K2HPO4, KH2PO4) sold to control pH.

The accepted definition of an acid/base is the "Brønsted–Lowry acid–base theory", although the "Lewis acids" are easier to understand. <http://en.wikipedia.org/wiki/Lewis_acids_and_bases>.

cheers Darrel


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