PH KH CO2 Relationship - The Planted Tank Forum
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post #1 of 16 (permalink) Old 01-31-2020, 05:44 PM Thread Starter
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PH KH CO2 Relationship

Something has had me stumped for a while now, I'm finding it difficult to search for an answer and I'm hoping someone here can help me with it? (search terms are just too short or general).

I'm happy with the charts showing the relationship between PH, KH and CO2.

But there is something I don't quite get..... why do many reputable websites/shops/people when listing water parameters for fish state that the KH should be high/alkaline, and then the PH relatively low/acidic


Are they assuming everyone is injecting CO2? Or am I missing something about the chemistry? In my low-tech planted tanks CO2 runs at about 0.5-2ppm (from the charts, not direct). So I have to keep my KH around 1dH to keep my PH anywhere near neutral!

For the record, I'm also totally in agreement that a stable PH/KH with plenty of water changes is far more important than it's exact value.



It's just I don't get why they would list two incompatible ranges when I assume most tanks out there are hum-drum, low-tech (probably unplanted) tanks?
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post #2 of 16 (permalink) Old 01-31-2020, 10:50 PM
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Originally Posted by AdamG View Post
[FONT=&quot]But there is something I don't quite get..... why do many reputable websites/shops/people when listing water parameters for fish state that the KH should be high/alkaline, and then the PH relatively low/acidic
Who is recommending this?

Makes little sense. High KH will by it's nature have high pH, unless something like an acid is driving it down. Can't imagine wanting to do that?


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post #3 of 16 (permalink) Old 01-31-2020, 10:54 PM
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I was wondering the same. If there's a particular site posting this it may be an error, ignorance, or translation from degree to PPM issue? Because I'm not sure how one would even go about keeping a consistent high KH, low pH tank.
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post #4 of 16 (permalink) Old 01-31-2020, 11:33 PM
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I've never heard this recommendation online or not. In fact, most non aquascape fish shops dont even know of this relationship in the first place.
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post #5 of 16 (permalink) Old 02-01-2020, 01:03 PM Thread Starter
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Well I can't say this is true for all the different care recommendations for all fish, but here are a few links to the fish in my tanks:


Ember Tetra:
https://aquaticarts.com/products/ember-tetra [KH 3-12dH, PH 5.0-7.0]
https://www.liveaquaria.com/product/3511/?pcatid=3511 [KH 4-8dH, PH 5.5-7.0]


Corydoras:
https://aquaticarts.com/products/ora...n-cory-catfish [KH 2-15dH, PH 6.0-7.5]

https://www.liveaquaria.com/product/846/?pcatid=846 [KH 0-15dH, PH 6.2-7.8]


RCS:
https://flipaquatics.com/products/co...=3142127681576 [KH 2-8dH, PH 7.0-7.6]
https://theaquariumadviser.com/shrim...parameters/#pH [KH 1-4dH, PH 6.5-7.5]


Zebra Danio:
https://www.aqueon.com/information/care-sheets/danio [KH 3-8dH, PH 7.0-7.8]
https://www.aquariumdomain.com/adSoc...p/zebra-danio/ [KH 8-12dH, PH 6.0-7.8]
Zebra Longfin Danio - Seahorse Aquariums Ltd [KH 8-12dH, PH 6.5-7.0]


American Flagfish:
https://www.liveaquaria.com/product/2776/?pcatid=2776 [KH 6-20dH, PH 6.7-8.2]
https://www.petguide.com/breeds/fish/flagfish/ [KH 6-20dH, PH 6.7-8.2]


Otocinclus:
https://flipaquatics.com/products/ot...=3810834546728 [KH 4-7dH, PH 7.2-7.5]
https://www.aquariumdomain.com/adSoc...nclus-catfish/ [KH 6-10dH, PH 6.5-7.5]


I'm starting to think that somewhere along the line some people have gotten confused between GH & KH on these links?



In general I would say that the forums are better when searching, but I've still come across posts that people are adamant that the KH should not go below 2, and the PH should be acidic (below 7.0):
https://www.tropicalfishforums.co.uk...?topic=46554.0 [(Stephen's posts) KH 2-4dH, PH 6.2-6.8]


I think the thing that bugs me the most is that when I was looking for compatible tank mates and I spent a lot of time researching water parameters for fish (before I understood the KH, PH, CO2 relationship). I genuinely thought that all these fish would work together, all I needed to do was to set my KH to about 5, and my PH to about 7.0!!!


I have now had to start running other tanks because the Flagfish and Danios really do need a higher KH (4+, PH 8.2+) to look their best, and the rest need a lower KH (~1, PH ~7.0). I'm still not sure what the Oto's prefer, they don't appear to be stressed in either water (when transitioned over several weeks of 10% wc).


I suppose I wanted to know if anyone else had noticed this and/or if there was something I was missing about the chemistry?
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post #6 of 16 (permalink) Old 02-01-2020, 04:02 PM
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Those look like pretty wide ranges and many of those fish come from naturally acidic water. I could tell you from experience that my tap KH is 2 and it was pushed down to zero with aquasoil and I've kept embers, otos, endlers, RCS with the KH of 0. My current tank has Seiryu stone that raises my KH to 8 and I'm keeping the same fish perfectly.


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post #7 of 16 (permalink) Old 02-01-2020, 04:11 PM
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perhaps, its also interesting to realize some of the new information points more to maintaining a consistency in your water parameters (aside from co2 ph swings) instead of chasing a certain ph. this is probably more true when you see a range of acceptable values for your fish selection .


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post #8 of 16 (permalink) Old 02-01-2020, 04:42 PM Thread Starter
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Those look like pretty wide ranges and many of those fish come from naturally acidic water. I could tell you from experience that my tap KH is 2 and it was pushed down to zero with aquasoil and I've kept embers, otos, endlers, RCS with the KH of 0. My current tank has Seiryu stone that raises my KH to 8 and I'm keeping the same fish perfectly.
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perhaps, its also interesting to realize some of the new information points more to maintaining a consistency in your water parameters (aside from co2 ph swings) instead of chasing a certain ph. this is probably more true when you see a range of acceptable values for your fish selection .

Sure, I totally agree that stable & clean water is more important than hitting any particular KH, and resulting PH.

I have though seen that my Embers and Ven Corys have noticeably better colour with a lower KH (~1), and my Flagfish have better colour with a higher (relatively, 4+) although YMMV.

I suppose my beef is with the two stated ranges being incompatible unless some serious CO2 injection is being used?
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post #9 of 16 (permalink) Old 02-01-2020, 05:26 PM
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I don't know if it's the KH, since my embers I think have pretty good color at a KH of 8.


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post #10 of 16 (permalink) Old 02-01-2020, 05:52 PM Thread Starter
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I don't know if it's the KH, since my embers I think have pretty good color at a KH of 8.

Sure..... and I guess your PH is around the 8.1 to 8.5 if your running low-tech?

And to sound patronising (which really isn't my intent) what water parameters would you put down if you were writing an Ember keeping guide?

My point is that there are more than a few references on the web that state for example that Embers should be kept at a PH of around 5.5 to 7.0, and then state that the KH should be in the 3-12 dH range. For most people without CO2 injection (and a couple of plants) the lowest PH they could realistically achieve with a KH of 3 is about 7.6! (CO2 @ 2.0ppm). And I don't think its an isolated example, I seem to be able to find these contradictions for all of the fish I keep (although I will admit that there are some care sheets out there with far more realistic KH-PH ranges).


All of that is AFAIAA? I'm still thinking that there might have been something that I have missed?

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post #11 of 16 (permalink) Old 02-01-2020, 06:24 PM
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.Sure..... and I guess your PH is around the 8.1 to 8.5 if your running low-tech?
My tank PH is around 6.6, my tap is around 7.5 (I run co2). I can only tell you I've kept embers between a PH of 6.5 to 7.5 and a KH of 0 to 8 and all was good. Water quality to me is the most important.

My current tank is the link in my sig. Some of the more recent pages will show my embers.

I think many of the care sheet numbers and what's important are very dated. Water quality to me is the most important. I bought my embers locally and they were in KH of 2, I only temp acclimated them for 15 minutes and dumped them into my tank with a KH of 7-8 and I haven't lost any of them yet. It's been a few months.


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post #12 of 16 (permalink) Old 02-01-2020, 07:33 PM Thread Starter
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My tank PH is around 6.6, my tap is around 7.5 (I run co2). I can only tell you I've kept embers between a PH of 6.5 to 7.5 and a KH of 0 to 8 and all was good. Water quality to me is the most important.

I do agree with you



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(I run co2).

I think this is where we have our wires crossed slightly. I am in particular talking in relation to low-tech tanks. (What I assume to be the vast majority of tanks in the world.)
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post #13 of 16 (permalink) Old 02-01-2020, 08:20 PM
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To add more personal experience... I have and have had multiple different fish with varying requirements in my tank at the same time. I've ran it as low as 6.5 ph and as high as 8.0. 0 kh (due to aquasoil) and 12 kh (due to seiryu stone).

The fish never care. However, shrimp died at 0kh within a day of putting them in every time.
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post #14 of 16 (permalink) Old 02-06-2020, 03:31 PM
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A bit technical but possibly helpful none the less...

https://www.thekrib.com/Plants/CO2/caco3.html

If you read through it I'd be curious to know your thoughts.
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post #15 of 16 (permalink) Old 02-11-2020, 09:52 PM Thread Starter
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A bit technical but possibly helpful none the less...

https://www.thekrib.com/Plants/CO2/caco3.html

If you read through it I'd be curious to know your thoughts.

Hi and thanks for your post. I did have a read....... it was somewhat interesting, but it hasn't shed any further light for me.

I'll try and summarise my main points/statement/question to try to be more coincidence:-

- I agree that stable, clean water is far more important than hitting a particular PH
- I found researching for my community tank there were some incompatible ranges of PH & KH on many of the websites. i.e. KH 3-12dH, PH 5.0-7.0
- AFAIAA a PH of 7.0 or below is unattainable with a KH of 3 or above in a non-injected tank (most tanks out there)
- Quite simply there are lots of websites out there giving out information that is just plain wrong? This doesn’t surprise me that much, but as I could find so many examples, I asked the question to see if was missing some vital bit of info or not?
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