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Question for ceg4048

markk said:
for CO2 @ 30ppm
- kH 1: pH = 6.0
- kH 4: pH = 6.6
Have I got that wrong?
or do I need some fresh air
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Not sure what youre doing. You are supposed to do from pH at equilibrium (which is whatever pH has a CO2 ppm of around 1.5) down to the pH at which you get 30 ppm CO2. This for each kh that you want.

I think what you are doing is comparing the pH for 30 ppm CO2 for each kH. This is not what I mean.
What I mean is the "jump" of pH for the same water (not at different khs)
 
Jose said:
I think what you are doing is comparing the pH for 30 ppm CO2 for each kH. This is not what I mean.
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But that is exactly what you've referred to in the quoted thread - and that is what I was responding to.

For clarity, this is the text I'm referring to.

here are his exact words from another one:

"Say you have 30ppm CO2 in a KH of 10 and a 30ppm CO2 in a KH of 1.

The pH difference is? 1.0 pH units.

6.0 vs 7.0 pH.
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The 1.0 pH difference is entirely coincidental for the two kH solutions he has chosen.

Anyway...

For additional clarity, yes - you are correct about the consistent drop in pH across different solutions (i.e. kH is notionally irrelevant). I should have made that clearer earlier. Both Tom and ceg4084 are correct as well - they're just presenting it differently.

For the purposes of what you're trying to achieve, I can't help but think you're over analysing it. As you've already concluded, there may be too many other factors in aquarium/tap water to allow you to accurately predict the correct CO2 ppm using just the pH. If you go down that route, you'll be getting it 'about right' - which is fine - but you seem to want more.

The alternative is to remove the other variables/factors - which is essentially the beauty of the drop checker. 4kH solution and a pH indicator. It's not ideal; it takes a while to reach equilibrium with the tank water and you have to 'interpret' the colour of the solution. But again, it will be 'about right'. (You could get really fancy and stick your pH meter in the 4kH reference solution in the checker...)

Regards

Mark
 
Then why does Tom Barr recommend a 1 ph unit drop whatever your water is? Because this is true for most waters no matter what they have in it. 1 unit ph isnt a coincidental value. I recommend doing a search please.

Anyway hopefully someone will take the time to answer my question which is quite important since it makes a hell of a lot of difference.
 
Yes, people on this forum seem to be obsessed with a "1 point pH drop before lights on". It's just an arbitrary calculation that depends entirely on the individual tank, I don't even bother testing my pH any more.
 
Sacha said:
Yes, people on this forum seem to be obsessed with a "1 point pH drop before lights on". It's just an arbitrary calculation that depends entirely on the individual tank, I don't even bother testing my pH any more.
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Its not arbitrary. Go to thebarrreport.com and do a search.

.....My questions remains unanswered:(.
 
Your question remains unanswered because you do not understand how the pH scale works. You seem to be denying the well-known fact that KH is a pH buffer.

It's a logorithmic scale. 30ppm of Co2 in a tank of KH 1 might drop the pH by 1, but the same concentration of Co2 in a tank of KH 10 will only drop the pH by about 0.3 or so.

So a "Full pH drop before lights on" in a tank with KH 15 will most likely kill all of your fish.

Furthermore, the Co2 concentration at the beginning of the injection period is rarely zero. So I you don't know what your concentration is to start with, how on earth do you work out when you have 30PPM?

Finally, there are *many* other factors aside from carbonic acid that affect pH.
 
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Jose said:
I have done it. Its always around 1 unit pH. Its not coincidence. You arent reading the table properly then.
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What are you even talking about? Don't you understand that KH buffers the pH? The higher the KH, the less your pH drop will be with the same amount of carbonic acid dissolved in the water. It's ok if you want to deny this and say it's a lie, you'll just be wrong :)
 
I wont go through the same things again with you Sacha. Co2 is not an acid in itself but it creates an acid when in solution, this is why its behaviour is different. Its has been tried and tested (the 1 ph drop for different kh waters). This being said I dont think your ways are even worth answering to. Im just interested in the answers but I can see most people prefer to stay in their confort zone so....

Its not always a 1 pH change. It can vary a bit I suppose depending on the buffers in your water. But it definately doesnt vary as much as cegs example. Its normally around 1 unit of pH, and normally not less than that.

Id really like to hear what ceg has to say on this;).
 
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markk said:
Jose
One last go from me Please don't bite!
Sacha hit the nail on the head - the 1.0 pH figure is arbitrary.
For most people with water within reasonable parameters, dropping the pH by about 1point will give you about 30ppm CO2 with relatively little risk.
Have a look at:-
http://www.plantedtank.net/forums/showpost.php?p=4677466&postcount=7
regards
Mark
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Youre are proving my point Markk. I never said it had to be exactly 1 ph unit (If I did I apologise) but around it. Definately not the 0.2 or 0.4 that ceg suggests. Kh has a minuscule effect on that (ph drop needed) and this is what my question was.

I know what you mean with the link though. Its not exactly 1 unit all the time buts it varies around 1-1.4.

So in practical terms: You take tank 1 and let water rest in a glass. Measure its pH. Then add co2 in the tank until you get a 1 unit ph drop in the tank.
Then take tank 2 (different kh) and do exactly the same.
You should get pretty much the same CO2 ppm for both if youre doing exactly the same.
At least this is very true if you do the ph/kh table example. And the ph kh table isnt real life but its a way to compare dferent khs.

I dont want to argue about exact numbers just the idea (see my question) about different khs and same pH drop (aprox).
 
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http://www.barrreport.com/forum/barr-report/co2-enrichment/3097-ph-drop-co2-chart
Its inacurate as a method yes but its not bad to get an idea of the pH drop you need. It shouldnt be 0.2 or 0.4. at all.

So the questions is. If you have really hard water (like me 18kh), then do you not need as high a pH drop really?
If this were true you should be able to back it up with the pH/kh table doing the example for the extremes (say 2kh and and 19 kh). It turns out that you need exactly the same pH drop(this value is different depending on what equilibrium level you choose but its the same for both khs)
 
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alkalinity (which is what KH measures) is the ability of a mixture to counter acidic change. Therefore two solutions with the same pH but different alkalinity will give different pH drops, given the addition of an equal amount of H+ ions (from an equal amount of CO2 forming carbonic acid I presume). Buffering.

The table indicates that Hobbyist A (0.2 pH drop person) has 18.9 ppm in his tapwater. This clearly isn't the case, as I mentioned in my first post. So now you have two possibilities:

  1. It is impossible to have pH 7.2 tapwater with KH 10---> the table is correct and the water would have much higher pH
  2. It is possible to have pH 7.2 tapwater with KH 10---> the table is wrong

The problem with #2 is that you're then asking people to use the table to prove that the table is wrong.


All I've really decided is that I'm going to measure my pH with a drop checker lol
 
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