What's the deal with kH/Alkalinity?

cbaum86

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So, first off I guess really we're talking alkalinity and not really kH but hey ho. Whilst I'm not really interested in adjusting my kH, it is fairly low around the 3 mark and it works fine for me, I keep seeing, in forums, social media groups and websites recommendations to raise this up. I am more interested in why this would keep being recommended rather than actually doing it.

Now, I understand the purpose of buffering against the oh so dreaded pH drop *shudder* and what not but if between water changes you're not seeing a tremendous fall in pH (apart from the daily one due to co2) and you still have some reading of alkalinity left before the change is there any need to raise it?

Are there different guidelines on how much to care about the alkalinity in a planted tank as oppose to a fish tank with plants?

I guess certain species of fish would prefer higher kH values?

I mainly keep my tank on the motto 'if it looks healthy then it's all good' but I do like to understand why suggestions are made or the theory behind what I'm reading.
 

dw1305

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Hi all,
hilst I'm not really interested in adjusting my kH, it is fairly low around the 3 mark and it works fine for me, I keep seeing, in forums, social media groups and websites recommendations to raise this up. I am more interested in why this would keep being recommended rather than actually doing it.
Some of the advice is a left over from when people didn't ever change their tank water, if you don't have water changes microbial nitrification will eventually use up all the carbonate hardness, and you get <"old tank syndrome">. Another, historical reason, for having higher carbonate hardness was that the nitrifying filter bacteria were thought to need hard water, and a constant source of ammonia, otherwise they died and your tank became non-cycled and crashed.

Neither of these arguments are really relevant now, water changes are pretty much universal among tank keepers, and we know that nitrification is carried out by a much wider range of organisms than was thought, with the high pH/high ammonia/high carbonate hardness bacteria being, at most, very minor players.

As planted tank keepers we have the added advantage of having "plant/microbe biofiltration", which has a number of advantages over "microbe only" filtration. Have a look at the linked threads in <"Low Energy......"> for some references etc.
Now, I understand the purpose of buffering against the oh so dreaded pH drop *shudder* and what not but if between water changes you're not seeing a tremendous fall in pH (apart from the daily one due to co2) and you still have some reading of alkalinity left before the change is there any need to raise it?
You don't need to raise the dKH.

There are a number of difficulties with pH measurement and interpretation, pH is both a ratio and a <"log10 scale">.

Stable pH only exists in very heavily buffered water. As you approach pure H2O pH becomes less and less meaningful. In soft waters pH will always be a movable feast, and you can't extrapolate from sea water or Lake Tanganyika to soft water.
I look on changes in pH in another way, I just say "does this change in pH reflect a large change in the chemistry (number of ions) in the water?"

As long as the answer is "no" (like in your added CO2 scenario) then it isn't going to bother the fish. Have a look at the <"A question, dissolved...> thread for an example of pH fluctuations due to dissolved gases.

cheers Darrel
 

cbaum86

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Cheers Darrel. I was hoping you'd pop up with an answer as I often read over your posts and links several times trying to fathom exactly what it all means.

I have no intention of trying to change my dKH or care (to a certain extent) that my pH drops with co2 injection as I "think" I understand - maybe not all the chemistry, why that is nothing be scared of.

I simply wondered if there were a chemical/biological reason why certain people jumped to suggesting tanks should raise their KH. It seems, that as I suspected with tank maintenance and water changes a low KH is managed and doesn't need to be raised.
 

dw1305

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Hi all,
I often read over your posts and links several times trying to fathom exactly what it all means.
That is often the issue. I'm not a chemist and I had to get people who understood the chemistry to explain it to me (in terms I could understand) before I could join up all the dots.

From a personal point of view, I think I found pH and buffering the most difficult concepts, because even though I knew what the definitions were I didn't understand what they meant in practice.
I simply wondered if there were a chemical/biological reason why certain people jumped to suggesting tanks should raise their KH. It seems, that as I suspected with tank maintenance and water changes a low KH is managed and doesn't need to be raised.
It is really the pH stability thing, that is partially why I like electrical conductivity as a measurement if you have a low electrical conductivity (below 150 microS ~ 100 ppm TDS) you don't have many ions of any description and pH is going to be a movable feast.

As soon as you know that fish are quite happy with a rapid pH fall when you add CO2 and an equally rapid rise when you turn it off you can tell that it isn't the pH changes themselves that bother the fish, and that acidosis and fish death are both symptoms of underlying problems, rather than one causing the other.

cheers Darrel
 
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