CO2/pH/KH table

ua hua

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I haven't really tested my tank in a long time and after having problems with a few plants showing signs of co2 deficiency I decided to test tonight. Now I knew I had high kH but after testing tonight I think I might need to start mixing ro water with my tap.

Here is my parameters:

kH: 12
gH: 5
pH: 6.8

According to the charts I have 57.1 ppm of co2. I have a wet/dry and what I would consider ample surface agitation and my fish never show any signs of stress from the co2. I quit using my drop checker for reference a long time ago as it is always bright yellow by the end of the day but for some reason I feel that I'm not getting enough co2 into the tank. I have tried 3 different diffusion methods not a one which I have settled on yet. I will not go back to the needle wheel pump feeding right into the tank as the micro bubbles are not to my liking. Most recently after running dual venturi method off my reactor I tried running the reactor post needle wheel pump but didn't notice much of a change. Will lowering my kh by mixing with r.o. water be a smart decision or am I fine just leaving it where it is? I would love to be able to keep rotala macrandra but have had no luck with that plant and assume it doesn't like higher kH. Ideally I think a kH of around 6-8 would be better.
 

Tom Barr

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Worth a shot to drop the KH to about 3-4, you should see some differences.
You'll need to add the GH booster however.

When is the pH taken?

Also, the higher KH's, the more possible error you have with KH.
And the difference in 1 degree of KH at say 8 vs 9 KH is a lot of CO2, vs KH of 1 vs 2 degrees as you get more and more CO2 into the system.

Folks need to know that as you approach the upper bounds with the CO2 dosing...........with fish, that it gets more touchy. It's not the same at lower levels of CO2. 0.1 pH change is only a 2-3 ppm at 15-20 ppm, vs say 8-10 ppm once you are up in the 40-50 ppm's (might not be exact, but should be relatively close)
 

Tug

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When I used DIY CO2 I just assumed I was providing low levels of CO2 so I never spent a lot of time trying to measure it. Now that I am using a pressurized CO2 setup I am trying to maintain between 30 & 40ppm of CO2 during the day. I do not have a KH test but the water taken from the tank, after sitting for over 24hrs, has a pH of 7.6 and in the tank, just before CO2 comes on, the pH is ~ 7.2 according to the API test kit and my eyeball. Currently, after the addition of CO2 and just before the lights come on, pH is ~ 6.8 (maybe even 6.6) and at days end I am reading ~ 6.4pH.

  • :stupid:
  • Does this drop in pH tell me anything without knowing my exact KH?
  • Where do I want my CO2 levels just before the lights provide around 60 PAR at the substrate?
  • Can I turn my lights on an hour earlier, using 1/3 or 1/4 as much light, when levels of CO2 are closer to 10-15ppm?
  • And, what happens when CO2 levels climb gradually, increasing from 10-15ppm (lights on) to 35ppm, by the end of the day?

    The fish do not seem stressed by days end so the actual level of CO2 may be lower then 35ppm but is it common to see a gradual climb in CO2 levels and does it mean anything?

The water quality report for DC shows alkalinity on average at 64ppm (I think that's 3.5 dKH).

DC Water Quality Test Results
http://www.dcwater.com/waterquality/test_results.cfm
 
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Detrius Maximus

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Jun 29, 2013
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Calculating CO2 Values Not on KH/CO2/pH Chart

Looks like for a given KH, the new CO2 ppm, (CO2_NEW(pH_NEW)) can be calculated by taking the given CO2 ppm: (CO2_GIVEN(pH_GIVEN))*10^((pH_GIVEN) - (pH_NEW)), where pH_NEW
 

Tom Barr

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Detrius Maximus;116864 said:
Looks like for a given KH, the new CO2 ppm, (CO2_NEW(pH_NEW)) can be calculated by taking the given CO2 ppm: (CO2_GIVEN(pH_GIVEN))*10^((pH_GIVEN) - (pH_NEW)), where pH_NEW
 

Tom Barr

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Detrius Maximus;116864 said:
Looks like for a given KH, the new CO2 ppm, (CO2_NEW(pH_NEW)) can be calculated by taking the given CO2 ppm: (CO2_GIVEN(pH_GIVEN))*10^((pH_GIVEN) - (pH_NEW)), where pH_NEW
 

dutchy

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No, simply because Excel is no CO2. It might help a bit in low CO2 applications, but can never replace it.
It's more an intermediate method between CO2 and non CO2 in the aspect of plant growth.
 

Detrius Maximus

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Tom Barr;116872 said:
Yes, pretty much........UNLESS.............can you think of several examples where this will no longer work well? I can think of 3 REAL examples.

The chart assumes any changes in pH are due solely to the addition of CO2 gas into the system and the KH is constant. So...

Immediately following a large water change...

1.There would be a dynamic shift in the tank pH where
wood/organic material releases acids to lower pH. This effect tapers off as the wood ages.


2.There would be a KH increase if carbonate sources dissolve (shells, limestone) and absorb H+, lowering [H+],
thus raising pH. This scenario is less likely (hopefully!) in freshwater systems with CO2 dosing since free [CO2]g decreases
with increasing pH. A wise hobbyist would eliminate this scenario.

Actual free CO2 levels in a well-maintained, mature tank (wood has been submerged for a long time) with non-carbonate rocks would more closely track/match the CO2 levels as predicted on the CO2/pH/KH table.

Oh, and I just noticed a linear relationship going DOWN the chart. Holding pH constant, the ratio of any two KH values equals the ratio of the associated free CO2 values.

For example, @pH = 7.0 ---> KH4/KH16 = 0.25 and CO2(KH4)/CO2(KH16) = 12/48 = 0.25.
 

BenFishin

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Is there a chart for KH in the 20's lol? I've got 18 out of the tap and 21 in the tank. Ph 7.8 in the morning. I can get it to about 6.2 but fish gasp, I back off to 6.6 as I have had things fail and had build up of CO2 in the past. I leaving a little wiggle room at 6.6 and fish and plants look happy.

My drop checker with tank water in it is dark green at this point. (I know, I know I'm supposed to use 4 dkh RO but if it is calibrated with tank water and know what colors are bad, I guess It shouldn't matter). I am in central Indiana on a well with old copper pipes (Toms Favorite ;) time for an RO unit.

Anyways back to the thread topic. That chart indicates my CO2 is 150+. Definitely fools carbonate in my tank.
 

BenFishin

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Is there a chart for KH in the 20's lol? I've got 18 out of the tap and 21 in the tank. Ph 7.8 in the morning. I can get it to about 6.2 but fish gasp, I back off to 6.6 as I have had things fail and had build up of CO2 in the past. I leaving a little wiggle room at 6.6 and fish and plants look happy.

My drop checker with tank water in it is dark green at this point. (I know, I know I'm supposed to use 4 dkh RO but if it is calibrated with tank water and know what colors are bad, I guess It shouldn't matter). I am in central Indiana on a well with old copper pipes (Toms Favorite ;) time for an RO unit.

Anyways back to the thread topic. That chart indicates my CO2 is 150+. Definitely fools carbonate in my tank.

Ben
 

lucci418

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I dont know why is KH,my KH is changing all the time.The meanning of KH is not the sum of all the calcium,it is the sum of -HCO3. GH is the sum of hardness of Ca + Mg.So what on earth is the parameter of hardness on this CO2 Table?Kh(-HCO3) or GH(general hardness of Ca and Mg)?I am totally confused…If Kh,why does my KH is always changing?13 on monday, 4 on saturday:confused:
 

Christophe

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Don't make a big deal of the KH/pH/CO2 chart -- it's based on some carbonate compound being the ONLY thing added to the water. Meanwhile, all the ferts we add have subtle effects on pH, not to mention all the organics & living things in there. It really isn't all that useful. Fresh Aquasoil will tend to buffer away some carbonate, if that's your substrate, that will end before too long.
 

rajkm

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If your KH is increasing its usually some limestone.
If it's decreasing then Aquasoil is buffering it out.

Don't worry about fluctuations in KH. Keep your CO2 injection rate constant. And adjust slowly. This is because if you are injecting 30ppm of CO2, no matter what KH, you have 30ppm of CO2

The only issue is dialing in the CO2. For that I recommend doing it on a day you are home and adjust your needle valve quarter turns at a time every 2-3 hours. If you see fish gasping, back off the last change. Let this run for a week and then try again, as fish do adjust to the PH fluctuations. If you are not able to increase it any further you should be close to your target CO2 or even more.
 

lucci418

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If your KH is increasing its usually some limestone.
If it's decreasing then Aquasoil is buffering it out.

Don't worry about fluctuations in KH. Keep your CO2 injection rate constant. And adjust slowly. This is because if you are injecting 30ppm of CO2, no matter what KH, you have 30ppm of CO2

The only issue is dialing in the CO2. For that I recommend doing it on a day you are home and adjust your needle valve quarter turns at a time every 2-3 hours. If you see fish gasping, back off the last change. Let this run for a week and then try again, as fish do adjust to the PH fluctuations. If you are not able to increase it any further you should be close to your target CO2 or even more.
Thanks a lot! I will try this method at home.
 

lucci418

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Don't make a big deal of the KH/pH/CO2 chart -- it's based on some carbonate compound being the ONLY thing added to the water. Meanwhile, all the ferts we add have subtle effects on pH, not to mention all the organics & living things in there. It really isn't all that useful. Fresh Aquasoil will tend to buffer away some carbonate, if that's your substrate, that will end before too long.
Thank you.I think I need focus on the growth of plants or some actual observation,but do not be so senstive to the values or some rigid methods. Method gives one direction but not cage:)
 

Hardwell

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Can someone clear up something for me, what if the water is just naturally acidic and soft and its already at a kh of 4 with a ph of 6.6, just means the water naturally has 30ppm co2? or is that never possible to have water like this without altering it with CO2.
 

Christophe

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Can someone clear up something for me, what if the water is just naturally acidic and soft and its already at a kh of 4 with a ph of 6.6, just means the water naturally has 30ppm co2? or is that never possible to have water like this without altering it with CO2.

This is the fundamental problem of using the pH/KH chart.
You can only get 30ppm CO2 by injecting it. if you don't add more CO2, all you'll have dissolved in the water is what will dissolve based on the ambient air CO2 content, something less than 1ppm.

Something else dissolved in your water is driving the pH a tiny bit lower by tending to release additional free H+ ions, or by binding OH- ions.
 

Hardwell

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This is the fundamental problem of using the pH/KH chart.
You can only get 30ppm CO2 by injecting it. if you don't add more CO2, all you'll have dissolved in the water is what will dissolve based on the ambient air CO2 content, something less than 1ppm.

Something else dissolved in your water is driving the pH a tiny bit lower by tending to release additional free H+ ions, or by binding OH- ions.

Thank you for the reply. Trying to fully understand the concept of all this. I consider myself intermediate in the high tech hobby, trying to be very experienced. My tank measures 4d KH and my pH is 7.2 without injection. I drop it down to 6.5-6.6 and I still don't see pearling. Tank looks like a soda pop can with fizz everywhere and my drop checker shows a light green. I want to drop it down further to 6.4 but im just hesitant, my gut is telling me no b/c it will gas my rummies. May try to do it on my day off to 6.4 and just watch my fish and plants closely. Any advice would be appreciated.

Note: This is a well circulated tank with no surface scum.