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How best to use a pH controller for pressurized CO2

Discussion in 'Equipment' started by ShadowMac, Apr 16, 2015.

  1. ShadowMac

    ShadowMac Moderator Staff Member

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    It is a question often asked by many hobbyists new to CO2. Should I use a pH controller? Many experienced plant keepers will tell you it is not necessary, I am one who agrees. However, CO2 is one of the most difficult parts of aquascaping to master. It is also one of the most crucial for ensuring healthy lush growth. A pH controller when used appropriately and when considering the various limitations of the method (as you should with all methods) it can be helpful in CO2 addition. I hope to outline a method I use to limit the shortfalls of using a pH controller and get healthy plant growth.

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    What is a pH controller?

    A pH controller uses a pH probe to measure the water pH and control the function of some other piece of equipment. In the case of growing plants it is used to turn on and off CO2 injection at a preset pH measurement. For our purposes, pH is simply a measurement on a logarithmic scale ranging from 0-14. 0 being the most acidic and 14 being the most alkaline. A quick breakdown of pH can be read here. As CO2 is added to the water it is dissolved by binding with water molecules creating carbonic acid. The increase in acid lowers the pH value.

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    KH and buffering capacity

    KH is a measure of carbonate hardness (CaCO3). Calcium carbonate acts as a buffer when CO2 is added to the water. It essentially neutralizes the additional acid preventing a change in pH. This does not, however, alter the amount of CO2 in the water, it simply prevents a large measurable change via a pH value. A buffer will not completely prevent the pH from moving. It will, however, reduce the range to which the pH will change when a given amount of acid (CO2) is added. For example, water with a low KH will show a larger pH drop when a certain amount of CO2 is added than water with a higher KH with the same amount of CO2 added. All buffers have a limited capacity meaning they can only absorb so much acid until the buffer is exhausted. At this point small amounts of acid can cause large changes in pH. This is why it is recommended to always have some level of KH in an aquarium. 4 dKH is generally the lowest recommended level to maintain good water stability and avoid a pH crash. It is essential to have a very good idea of the buffering capacity through a reliable high quality KH test in order to estimate your desired pH value and likewise desired CO2 concentration. Common hobbyist test kits are unreliable. I recommend a Lamotte KH titration test kit. It is very easy to use and has an indicator color that is easy to read and changes if you have added too much reagent letting you know to retest.

    A video tutorial on using a Lamotte test kit can be found here.

    The relationship between pH,KH, and CO2 ppm

    How does knowing pH and KH allow us to estimate our CO2 ppm? Let's look back, if we know adding CO2 changes our pH and that KH will absorb some of that change in pH we have two of three variables. When knowing two of three variables it is possible to solve for the third. This is where the math gets crazy, grab a pen, a calculator, and an abacus. You will need them.

    Just kidding...thankfully there are many charts available to use for reference. Here is a nice article from Tropica with a chart.

    The limitations of using pH, KH, and CO2 chart

    When referencing the chart it is important to keep in mind that there are a few limitations in using this method. The first being it assumes there are no other acids in the aquarium environment altering the pH. However, as many of you may know this is not the case. As with all biological systems, artificial or natural, there will be some sort of organic acids from biological processes and the decay of organic matter. Driftwood can leach tannins into the water, some aquarium planting soils also reduce pH. In short there are other things reducing the pH. The other assumption is that your KH remains stable. If you are using seiryu stone or another type of stone that has a tendency to alter water chemistry this will not be the case. Your buffering capacity can change over time. Both of these things can skew your estimation. Interestingly they counteract each other, but it is too difficult to estimate to what extent and would vary between systems.

    In order to reduce the margin of error from these limitations I measured my KH immediately before a water change (after 10 days), which measured 14 dKH. This particular scape has a large amount of seiryu stone. The measurement immediately after a water change was 7 dKH. Now I have an idea of how large of a swing I would expect to see. I felt the range was too large and have since begun doing two water changes per week in order to limit this swing and maintain a more stable KH.

    To compensate for additional unknown acids, I set the controller to a point two boxes lower than my target. This put the estimation into the red zone. Interestingly previously I was overdosing CO2 as compared to the controller method as measured by my yellow drop checker. It is now green.

    A final limitation to consider is the reliability and reference of your measuring equipment. How do I know my pH controller is good? It is important to regularly calibrate your controller using reference solutions. I also use a drop checker for a quick visual reference and second measurement. This way I may see something is wrong before it starts to manifest as algae or poor plant growth. Lastly, I used a handheld pH meter to corroborate my probes measurement. The handheld meter was independently calibrated and used one day after probe calibration. The two meters matched, increasing my confidence in the probe measurement.

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    A word on limitations of drop checkers: Drop checkers have a lag time in their reading meaning the color you see now may not be representative of the actual CO2 concentration at that moment. Drop checkers rely on the same pH, KH, CO2 relationship but do it within the drop checker. CO2 must degass into the drop checker and redissolve into the solution within the bulb. The subsequent change in pH causes the indicator solution to change color. This all takes time. It is further compromised by the method of CO2 distribution. Any methods that cause lots of CO2 bubbles like atomizers or diffusers will enter the chamber and cause an overestimation of CO2 concentration in the tank. For this reason, when using atomizers or diffusers and a drop checker I generally shoot for a more yellow green than if I were using a reactor. Also of importance is the location of your drop checker. It is best to locate it far from the source of CO2. I also try to place it in the position least likely to capture rising CO2 bubbles. These are areas of downcurents or behind an outlet.

    A nice article on drop checkers can be read here

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    Advantages to using a pH controller

    Using a pH controller may provide an aquarist with greater control, increased efficiency, and demands a greater understanding of CO2 and its relation to other factors fostering improved CO2 management. Prior to using the controller option I would simply inject at an estimated rate and observe if it was sufficient for plant health. I would use my fish as an indicator of too much CO2. My drop checker was yellow, fish behavior was not as active as it is now with reduced CO2 injection. Plant health has not suffered. It can sometimes be difficult to find a rate that provides adequate CO2 at lights on and yet does not begin to overdose CO2 as the light cycle progresses. A CO2 controller can allow for a reduced injection rate started earlier and then maintain the desired ppm of CO2 throughout the light cycle. I should mention there is no reason to turn CO2 on when the light is off with or without a controller.

    Information Page for pH and pH probes from Milwaukee Instruments

    pH info and probe testing

    See the probe test. A good way to determine if your probe is functioning appropriately or needs replacing

    Information on usage and storing from The Barr Report

    A brief word...

    I use less CO2 with what seems to be better results. One caveat to this improvement. Prior to using the pH controller feature I had purchased a PAR meter in order to dial in my lighting to the exact level I wanted it. Light is easily controlled, but hard to measure without a PAR meter. Once the light level is determined to be sufficient and not overkill, CO2 was easier to get right. Light is still the paramount factor in determining CO2 demand. Fortunately it is also the easiest to control.


    *I will continue to edit and update as time allows. I hope this is helpful to those wanting to try using a pH controller. All photos are my own. Finally, remember a successful planted aquarium/aquascape depends upon many factors: filtration/flow, CO2, light, fertilizing, and maintenance. Without all components working well together success is unlikely. There is usually more than one way to skin a cat, this is how I skinned the CO2 cat on my current 90 cm scape. Past scapes did not use this method.
     

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    Last edited: Apr 12, 2016
    Zeus, J Art, hgfx and 4 others like this.

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  2. greenfinger 2

    greenfinger 2 Active Aquascaper

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    Hi Shawn, Great info. Wonderful set up there:cool: Love the stainless steel diffuser :love::love:
     
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  3. nicpapa

    nicpapa Aspiring Aquascaper

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    I dont trust ph controllers ....
    They can calibrated correct but measure wrong....

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    Both 3 controllers calibrate correct.
    Both 3 have american marine pintpoint probe.
    The american marine ph , have the new probe.

    So how can you trust them .. :)
     
  4. ShadowMac

    ShadowMac Moderator Staff Member

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    This is the reason for secondary measures. A drop checker using a different method and a portable meter to corroborate the controller. Given the multiple measurements you have and the wide variation I would say there is either something wrong with the equipment or calibration fluid. Did you use two solutions to calibrate? A 7.0 reference solution should be used as the high calibration fluid and a 4.0 reference solution as the low. When I did mine both meters measured correctly. If this was not the case I would have to assume a problem with the equipment. I would recommend using a high quality lab grade probe as opposed to a cheaper hobbyist probe. The probes need to be stored in a storage solution when not being used and should never be allowed to dry out or the electrode may malfunction. When calibrating it is also important to give the probes enough time to settle before locking in the calibration.

    How do you know they calibrated correctly? I would place the meters into a reference solution and see what they measure after calibration as well. This may give some indication of which is malfunctioning. In my opinion the errors seen in your post need to be troubleshot and faulty equipment or calibration procedures identified. You could also swap probes to other meters, etc. to help identify what piece is faulty.
     
  5. nicpapa

    nicpapa Aspiring Aquascaper

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    yes i use two solution for calibration, ph 4 and ph 7 .
    The new probe is on american marine ph meter, if i swap the new probe to other ph meters and calibrate, they measure the same as america marine ph meter.
    Ph meters work correct the problem is on the old probes...
    But i saw that the old probes calibrated correct, but measure wrong....
    So if you want to trust them you must buy a new probe every year.
     
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  6. ShadowMac

    ShadowMac Moderator Staff Member

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    Yes, you are right. To ensure probes are working properly they must be replaced annually. My lab grade probe needs replacement every 18 months.
     
  7. nicpapa

    nicpapa Aspiring Aquascaper

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    what probe are you using?

    So after trying all methods of co2 adding in aquarium.

    I prefer for small tanks 20-80 liters continious 24/7 with co2 glass diffusers.

    And for bigers tanks , diy diffuse , like Rex Reactor, with magetic valve opening before lights and close before close the lights.

    I use the ph meter only for read the drop of the ph amd compines the tanks.

    The ph Controllers not working well for planted tanks.

    You know that the table ph kh co2 , is right only in a glass of water.
    Ph change from subtrates , wood and accid in the water.
    And kh test dont measure the true kh... it measure alkalinity .

    The best method for me is to read the plants growns and how the fish respond.
     
  8. Icethunder

    Icethunder Aspiring Aquascaper

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    (y);)
     
  9. ShadowMac

    ShadowMac Moderator Staff Member

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    The post here addresses these issues. As I said in the post, which I'm not sure you read all of, there are limitations to the method. There are also limitations to other methods. Some people want to use a pH controller and I tried to outline a best practice for doing so. I did not claim it was foolproof.

    As I said in the original post, a hobbyist grade kit is not a good choice. The lamotte test measures true KH as it relates to buffering capacity (CaCO3). I also mentioned there are other factors that affect pH that can change over time and to consider those. I really think you should try to reread the original post as I have addressed the issues you bring up there.

    Many would disagree with your method of 24/7 diffusion in a nano. Does it mean it is wrong? Not necessarily. As far as I am concerned a wrong method is one that does not get good results. In this hobby we must always be willing to assess our methods and look to a way that leads to success.

    Reactors work best with a pH controller and also with a drop checker. Using the fish observation it is easy to overdose CO2, in my experience.

    I have a 90 cm aquascape that would disagree with your conclusion pH controllers do not work for a planted tank.

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  10. ShadowMac

    ShadowMac Moderator Staff Member

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    The photo of the dropchecker is also in the 90 cm where a pH controller is used. Lots of healthy growth.

    The point of the original post was not to argue about what people think is best, rather to describe how best to use the pH controller method if one chose it. I have a feeling you did not read the entirety of the post, instead simply responded to the title.
     
    Last edited: Apr 20, 2015
  11. ShadowMac

    ShadowMac Moderator Staff Member

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    I am using a neptune systems lab grade probe. Replacement is every 18 months.
     
  12. nicpapa

    nicpapa Aspiring Aquascaper

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    Hi there....
    Sorry , you are correct , in first time i read it fast...
    I dont speak good english, and sometimes i read it wrong.

    Now I read it again.

    All those i wrote above , is after trying in my tanks, and how i had the best results.

    I keep 11 tanks and 9 of thems have co2.
    In small tanks i keep shrimps.

    I run 2 -3 years before my 180 liter tank with the ph controller, i use only the read of the ph and i follow the table for co2.
    It working well until the probe begin to read wrong, and adding litle co2 in the tank. ( that is the reason i cant trust them)

    As i read again your method is good, you compine two ph probes and a drop checker.

    So if i understand corect , when you use subtrates like ada, akadama, with a Kh3 you find the ph you need with the read of drop checker?

    Sorry again was mine mistake...

    Maybe one day i try your method .. :)

    Tank running wiht ph contrlollers was this

    http://showcase.aquatic-gardeners.org/2012/Big/3220.jpg
     
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  13. nicpapa

    nicpapa Aspiring Aquascaper

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    Have you ever combine ph result with american marine probes?
     
  14. ShadowMac

    ShadowMac Moderator Staff Member

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    I have never used American marine probes.
     
  15. ShadowMac

    ShadowMac Moderator Staff Member

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    This being an international forum I understand some things will get lost in the translation. No problem, my friend. I love the fact his forum has hobbyists from around the world. I certainly cannot speak a bit of Greek, let alone any other language. I'm fortunate so many can speak at least a little English.

    I use the drop checker as a quick visual reference. I look to see if it is at least green. It will not be a good measure of pH since the color gradient is subjective. It is simply a quick double check. Redundancy helps prevent a single malfunctioning device from screwing up the whole measure and causing a problem. I use the second handheld probe to check the calibration of the probe for the controller. I am not sure of the frequency of replacement for this device, so I will probably test to see if it goes bad at the one year mark. If the two probes match I assume they are functioning appropriately. If they disagree, I know one of them or both of them are nut functioning appropriately. I can then run a test to see if the probe is bad.
     
  16. ShadowMac

    ShadowMac Moderator Staff Member

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    Expected results

    This last week I did not manage to get to my second water change and missed the weekly by a couple days. My measures and drop checker performed as expected. My pH probe maintained the pH at the setpoint, however due to the climbing KH due to the Seiryu stone, the buffering capacity increased. I did not measure KH to determine exactly how much, but I had the previously measured range and it would most likely have fallen within that range. As a result of the increased buffering capacity, more CO2 was being injected into the system in order to hit the target pH. I could see my drop checker moving from a definite green to a more yellow-green. This is exactly what would be expected.

    Why is this worth noting? The value of understanding our process is to be able to provide reliable predictability. If things proceed as we would have expected it can help verify the system is functioning appropriately and that our understanding is accurate. It is another verification the pH probe is working, the measures and targets are correct, and the system variables change over time as expected. If the drop checker became more blue over time and the pH remained the same I could assume one of the two measuring devices is not functioning since it did not behave as expected. Either the solution in the drop checker is bad (unlikely) or the probe is malfunctioning. Troubleshooting will solve the problem. I'd replace the drop checker fluid and recalibrate and/or test the probe to determine if it was bad.
     
  17. nicpapa

    nicpapa Aspiring Aquascaper

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    Why are you using thsose rocks?

    I think with the method you are using co2 its not very accuracy if you see the drop checker. ( mostly if your substate lowering ph ) what the diference if you run it 24/7 or with magnetic valve.... :)

    drop checker measures
    • blue we have less than 20 ppm co2
    • green 25-40 ppm
    • And yellow ~50ppm.

    I want to read this and tell me what the beter method.:)

    http://www.prirodni-akvarium.cz/en/technikaCO2nastaveni

    With all methods you can grow all the plants.
     
    Last edited: Apr 24, 2015
  18. ShadowMac

    ShadowMac Moderator Staff Member

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    The soil is probably not dropping the pH much anymore since it is over a year old. Substrate tends to reduce pH which would make CO2 addition by pH controller fall short, likewise stones like Seiryu leach CaCo3 into the water and increase buffering capacity which leads to more CO2 being used. My method examined the range of drift in my KH from the stones over the course of the week. I also selected a target pH below my desired ppm to estimate a degree to which additional acids may be affecting pH. As I noted things behaved as expected. Observation is also important, if things are not going well the method should be reexamined.

    I think you are misunderstanding. The drop checker is not attempting to measure ppm, it is simply a visual double check for what the probe is telling me my CO2 concentration would be. By nature the drop checker is not accurate considering the range is so wide and the delay so long. It is keeping tabs on the controller and CO2. Another safety measure is that my bubble rate is not faster than it was when I was continuously injecting CO2 throughout the light cycle, so even if the buffering from the stones keeps the CO2 on, it shouldn't overdose to a lethal degree.

    The reason for redundancy in measuring is to detect problems if one should arise. By nature this is an estimation not an exact measure. All of the options available to us are imperfect.

    The article is good and outlines the advantages and disadvantages of some methods well. Thanks for sharing it. The important thing is to understand what the limitations of each method is in order to better inject CO2.

    By running 24/7 you are just wasting CO2. It is not needed when the lights are off. The reason the person in the article tested 24/7 was due to the slow rate not building to the target level quick enough, and if you increased the rate, the CO2 would spike above the target level. Running 24/7 allowed it to reach target level and stay relatively within that range. Although the author of the article noted there was an increase of about 3 ppm each day.

    It is also important to notice that our tanks are not all the same and even those conditions can change over time. For example, evaporating water can lead to increased degassing which could result in CO2 falling short. This has certainly happened to me. This is an advantage a pH controller has over the other methods, it can adjust injection to consistently hit the target. Its limitation is the fluctuation in water parameters over time. A good water change and maintenance routine limits this fluctuation and as I said in an earlier post there is some predictability in that change.
     
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  19. nicpapa

    nicpapa Aspiring Aquascaper

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    Haha , now you can add those you write in the article above. :)
    Because no ones write in your article, i must write something to explain it more. ;)
     
  20. greenfinger 2

    greenfinger 2 Active Aquascaper

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    Hi, I would reply :D But this thread is fantastic for us less knowledgeable people ;)


    I am still on the learning curve and learning all I can :):coffee::coffee: Looking forward to all the updates (y)
     

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