# CO2 - Lets Finalize this - pH meter, KH, ppm...



## Aqguy (Oct 30, 2013)

I just set my ph controller to my preferred ph number 6.6 and leave it there no timer runs 24/7, I control the c02 ppm buy adjusting the bubble flow count and reg pressure, got it were it would run pretty much all day and then cycle at night with the lights off.
A lot of people on here light a timer to turn the c02 off , however I prefer a steady ph and ppm always a condescend number this way.


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## samee (Oct 14, 2011)

Well Im trying to determine the proper ph and not eye balling it. I also need to know the min. amount I can dose so I dont waste so much co2.


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## Hardstuff (Oct 13, 2012)

For what its worth. I recently started to run my CO2 24/7, BUT it turns off for mini cycles mostly at night. It runs about 18 hours a day on average. I have found out my tanks do better with more stable PH less bounce in ph. Now in the morning the tank does not lag & I never come up short when the lights turn on. I learned this trick from my DIY CO2 tank. The plants always grew better in that tank even though I time out the reactor a few times a day. 
Bottom line , for me the CO2 stays more stable with the CO2 running more often. However you must know your tank & livestock before trying this. I balance the CO2 with proper surface agitation. 
I know people will say I am wasting gas but my tanks BBA is down 95-98% since I started doing this & the plants & fish seem healthier. 
Measuring CO2 can be tricky , I use just the ph & kh method & back that up with a digital ph meter. That being said I do not run wood or Aquasoil that could alter my readings so I trust this method. 
Hope this helps.
Also, I do not use a controller, its all manual but using timers.


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## samee (Oct 14, 2011)

Sorry its not helping. I need to know from someone know knows what Im talking about. Ive reduced my co2 to 6.4. Ill see what happens. Should be fine. Would really like it if someone could assure me.


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## Zorfox (Jun 24, 2012)

As you probably already know PH/KH relationship is not an entirely accurate way to measure CO2 concentration. There are other buffers which can affect this measure. That said if you want to find the minimum CO2 level reduce it slowly over time until you see changes, decreased growth, failing plant health, increase in algae etc. When you see a change that will be the minimum for your tank. I wouldn't try and come up with an arbitrary number and go with it. Instead, watch your tank and when you see those changes bump the CO2 back to the previous PH level. That should be the minimum CO2 level for your tank at that time. That level can change over time though so keep an eye out for other signs of CO2 deficiencies.


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## HUNTER (Sep 4, 2012)

Tom Barr suggested that PH/KH is the only reliable method of measuring Co2 and not the drop checker, he knows his stuff.


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## Aqguy (Oct 30, 2013)

Hardstuff said:


> For what its worth. I recently started to run my CO2 24/7, BUT it turns off for mini cycles mostly at night. It runs about 18 hours a day on average. I have found out my tanks do better with more stable PH less bounce in ph. Now in the morning the tank does not lag & I never come up short when the lights turn on. I learned this trick from my DIY CO2 tank. The plants always grew better in that tank even though I time out the reactor a few times a day.
> Bottom line , for me the CO2 stays more stable with the CO2 running more often. However you must know your tank & livestock before trying this. I balance the CO2 with proper surface agitation.
> I know people will say I am wasting gas but my tanks BBA is down 95-98% since I started doing this & the plants & fish seem healthier.
> Measuring CO2 can be tricky , I use just the ph & kh method & back that up with a digital ph meter. That being said I do not run wood or Aquasoil that could alter my readings so I trust this method.
> ...


Sounds right on a well balanced system this is what we strive for.
Green Leaf Aquariums said a staple c02 reading is important and I agree much easier to balance the tank/ readings without the swing of up and down.


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## dinnese (Feb 4, 2013)

When injecting CO2 into a planted tank, it is useful to know how much CO2 is actually getting dissolved into the water. Lucky for us, there is a simple way to calculate the CO2 level, based on the pH, and KH of the tank water. There is a fixed relationship between the pH, KH, and CO2 level. As you increase the amount of CO2 that is dissolved into the water, the pH will drop. And if you then stop adding CO2, the pH will climb as that extra CO2 is released from the water.

A little background science:
pH is a measure of the concentration of hydrogen ions [H+] in solution. pH is actually a logarithmic measure (-log[H+]). This formula has two implications. First, it means that the hydrogen ion concentration increases (thus the solution becomes more acidic) as the pH number decreases. Second, each time the pH is reduced by 1, the concentration of hydrogen ions increases by a factor of 10.

In more simple terms, the pH is simply a measure of the acidity or alkalinity of a solution. pH values from 0 to 7 are considered acids, and pH values from 7-14 are considered bases. 7 is neutral, neither an acid nor base.

As we add CO2 to water, it forms carbonic acid, which lowers the pH. The more CO2 that gets dissolved into the water, the lower the pH.

Working to raise the pH of the water is the KH. While KH refers to Carbonate Hardness, what is really measured by a standard KH test kit is really the buffering capacity. In "most" water sources, the buffering is provided by Carbonate. In that case, buffering capacity and KH are the same thing. Assuming a constant amount of CO2, a higher KH, will result in a higher pH.

Myth: A Low KH results in a larger pH swing when adding CO2.
Many people are under the mistaken impression that a low KH results in large pH swings when adding CO2, while raising the KH will result in smaller pH swings. This is not the case. The KH will move the start and end pH values, but the pH swing will be the same for a given level of CO2. You can see this in the chart below, or using the calculation:

Case 1: Assume a KH of 15 degrees, and a starting CO2 level of 4.5ppm, which would result in a pH of 8.0. If we then add CO2, to increase the CO2 level to 28ppm, that would drop the pH down to 7.2, for a pH shift of .8.
Case 2: Assume a KH of just 1.5 degrees, and a starting CO2 level of 4.5ppm, which would result in a pH of 7.0. If we then add CO2, to increase the CO2 level to 28ppm, that would drop the pH down to 6.2, for a pH shift of .8, the exact same as in case 1.

One possible explanation for this myth is that many copies of this pH chart skip some of the higher pH values, for example, jumping from pH 7.4 to a pH of 8.0. If the reader didn't pay careful attention, they might mis-interpret the size of the pH swing. I specifically made sure to include all pH values, between 6 and 8, in steps of .2.

This relationship will break down at extremely low KH levels (below 1 degree), when there isn't enough carbonate to completely buffer the acids present. In that case, the pH can drop quickly and dramatically. But if the KH is 1 degree or higher, then the size of the pH swing when injecting CO2 will be determined only by the amount of CO2 dissolved in the water.

The pH-KH-CO2 Relationship
pH, KH, and CO2 have a fixed relationship as long as carbonate is the only buffer present (no phosphate buffers like pH-UP and- DOWN, Discus Buffer, etc). There are some parts of the country that have high levels of phosphates in their water supply. For those cases, determining CO2 levels will be difficult, as the phosphate will throw off the pH-KH-CO2 relationship, which means the CO2 charts and calculator below won't work. Note that the commercially available CO2 test kits will also be invalidated by the phosphates.

To determine your CO2 level based on the pH and KH, you can enter the values into the on-line calculator, or use the chart at the bottom of the page.

NOTE: If you aren't adding CO2 to your water, and the CO2 level based on the pH and KH indicates more than 5ppm, then it is very likely that some other buffer (such as phosphate) is present in your water. In an inhabited aquarium, the amount of CO2 produced by the fish will not have an effect on CO2 levels in the water. Any excess CO2 created by fish will dissipate into the air, leaving a fairly constant CO2 level of about 3-4ppm. If you test your pH and KH, and without adding any CO2, the chart says you've got 20ppm CO2, don't believe it.

In some case, water coming right from the tap can contain very high or very low levels of CO2. This can result in tap water with a high KH, and low pH. But, in just a few hours, that excess CO2 will dissipate from the water, leaving the normal 3-4ppm, and the pH will rise. Sometimes, the water might come from the tap with extremely little CO2, which can result in tap water with a low KH, and a very high pH. Again, after a few hours, the CO2 level will equalize, and the water will end up with 3-4ppm CO2.

CO2/pH/KH calculator and chart
NOTE: This calculator (and the chart based on this formula) will only work if your water is carbonate buffered. If your water contains high levels of phosphates, it will alter your water properties, and invalidate these CO2 calculations.
If you have measured your pH and KH, and want to know how much CO2 you have, enter the pH and KH here.

An alternate use for this calculator, or the chart below, would be to determine the "target" pH needed to achieve a certain amount of CO2. A desireable CO2 level is 10-25ppm (which is indicated in green on the chart). Levels below that don't provide optimum CO2 concentrations for high plant growth. CO2 concentrations over 25ppm can be harmful to the inhabitants of your tank. I typically shoot for 15ppm CO2. So, using the calculator, enter your KH, then try entering different pH values until it shows a CO2 level around 15ppm. Using the chart, just find the row that contains your KH, then go across until you find your desired CO2 level, then look to the top of the column to see what your "target" pH should be. Once you know that, you can adjust your CO2 injection to hit that target pH.


Myth: CO2 level can be adjusted simply by adding chemicals to alter the KH or pH.
This is a common misconception when using the CO2 / KH / pH table. It appears that by altering any parameter, the other values should move. But this is not true. Treat the pH value you see as a result. If you alter the KH, then the pH will move. If you alter the CO2 level, then the pH will move. The pH will always react to changes in either of the other two parameters.

Example: My water comes out of the tap with a KH of 3 degrees, and a pH of 7.6, which according to the the indicates a CO2 level of 2.3ppm. Looking at the chart, I might (incorrectly) assume that If I simply raised my KH to 10 degrees, I would end up with the same pH, but the CO2 level would now be 12ppm! How easy! I can add CO2 just by adding some baking soda to raise my KH.
BUT! it doesn't work that way. Instead, as I raise the KH, the pH will rise along with it, and the indicated CO2 level staying at it's 2.3ppm. In my case, if I raised the KH to 10 degrees,

You can not alter the KH levels other than by adding or removing carbonate. You can not alter the CO2 levels other than by adding or removing CO2.

Adding certain "pH altering additives" can cause much confusion as well. Additives like "Proper pH 7.0" which force the pH to a certain value completely invalidate the CO2 / KH / pH relationship. This is because these pH altering additives contain phosphates. Phosphates replace the carbonates in the buffering system. And the CO2 / KH / pH relationship is only valid in a system that is buffered by Carbonates.

There is on case I've seen where the addition of CO2 resulted in an increase in KH. This can happen when you have something in the tank that dissolves carbonate into the water. Seashells, crushed coral, and many gravels and rocks will do this. With the addition of CO2, the water turns more acidic, which will increase the dissolving of the minerals. It appears that increasing CO2 raises the KH, which isn't really the case. The dissolving minerals raise the KH, and the increase in KH results in an increase in pH. In a system using a pH probe and controller to regulate CO2 levels, this can have fatal consequences, since the pH controller will keep trying to lower the pH, but as more CO2 is dissolved, it lowers the pH, which raises the KH, which raises the pH. So you now have more CO2, but the same pH. So the controller adds even MORE co2. And it will keep going. So it's important to know your KH whenever using pH to judge CO2 levels.

I would also like to add that when a tank has a starting PH value of 7.6 at the beginning of the day (common for tap water in some area's) and by the end of the day we have an ending Ph of 6.4 it may not be detrimental to the your fish but it certainly is not healthy for them either.


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## Hoppy (Dec 24, 2005)

We can't measure the ppm of CO2 in our aquariums accurately, unless we pony up about $3000 for a professional CO2 measuring probe. So, it is pointless to try to measure it and depend on that measurement for anything other than a reference value so we can spot changes in ppm of CO2. It is possible to measure changes in ppm of CO2 fairly accurately.

A typical beginning user of pressurized CO2 will be worried most about the possibility of killing off all of the fish in his tank by over dosing the CO2. Having gone through this I know that it makes you hypersensitive to tiny changes in the behavior of the fish, always thinking that you might be seeing them as they start to die off. This makes us timid about raising the CO2 bubble rate, and quick to lower it. As a result we are far more likely to have our tank running with 5 ppm of CO2 than with 50 ppm. A drop checker is a crutch that lets us overcome that timidity.

We can use the drop checker to give us a visual indication that we have a significant amount of CO2 in the water, but not an overdose of it. It is a very inaccurate way to measure the ppm of CO2, but a good way to know that we have closer to 30 ppm than 5 ppm or 60 ppm.

Once we get over that timidity hurdle, and know that even though our fish seem to be behaving abnormally, they are unlikely to be suffering from the CO2, we can start trying to optimize the amount of CO2 we are using. We can do that by using the plants and fish as the indicator - very slowly, over a week or more of time, increasing the bubble rate of CO2 until the plants stop improving in growth and health, without the fish showing real distress from the CO2. It makes no difference whether the method we use for measuring the actual ppm of CO2 says we have 25 ppm or 100 ppm when the optimum level is reached, it is still the optimum level for our tank at its current plant mass, with the current fish load. Now, we can monitor the pH and KH and see changes from that level accurate enough to readjust the CO2 if necessary. And, then the drop checker is no longer of value, so we might as well store it until the next time we want to go through this.


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## plantbrain (Dec 15, 2003)

The pH controller is a problem if the KH or anything that adjust the pH is added to the tap water and you do not check and notice it............

This errors in too little CO2, or way too much, neither are good.
This is why you should not use a pH controller unless the KH in the tap water is stable or you add aquasoil or driftwood and other things that will slowly change the KH/pH of the water.

Which are a lot of hobbyist.

If you set the CO2 rate at a constant relative flow rate, say 100mls /5 minutes...... it does not matter what the tap changes are, or the chemicals added to adjust the tap water, or the driftwood or the sediment............

The CO2 rate will not change.

With a pH controller it can and will change. pH alone is not the only dependent variable, so you can get caught with your pants down if you are not careful, even if you test the KH.


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## samee (Oct 14, 2011)

wow, thanks for the huge amount of info. I still did not get all of it.

I lowered my co2 to 6.4 vs previous 6.2. My indicator stays at green now. Which means theres not enough co2. Ill let it go like this for another day and increase it slowly. I dont have any wood or fish. I only have flourite as gravel. So there should not be any buffers or things to mess around with the hardness. Should measure my tap water everyday for a week to see if the levels stay consistent? The last time I had fish, I pushed my co2 to 5.9 and my fish would gasp and a few times they were just floating. So I know thats the peak and a waste of co2. 6.2 seemed to be ideal but I want to see if I can reduce it a bit.


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## plantbrain (Dec 15, 2003)

Might be 5.9, but then again, some fish are more tolerant than others, a good clean surface will also provide more O2, so current and ripples can help a lot.

Still, I would only use this as a relative measure and the 5.9 last time might be 5.7 or 6.1 tomorrow.

The RATE of CO2 is what you really want to know, not a pH.
Say the tank used 50mls /300 seconds of CO2 gas.
This is entirely independent of pH/KH/Tannins, any other wonky stuff in the water that throws the pH/KH/CO2 chart off.

You have the skills already to dial in the CO2 to an optimal level. Stick with that and slow progressive adjustments using pH. But the pH measurements will move if your tap changes, which happens often times seasonally.


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