stemar Posted February 7, 2003 Report Share Posted February 7, 2003 Hi, Interested to know if anyone has built their own CO2 Controller or would be interested in contributing knowledge and experience. I am considering this 'little' project once I have my tank up and running. I am considering the Jim Hurley option on The Krib (with a few modifications) http://www.thekrib.com/Plants/CO2/hurley-co2.html Stephanie Quote Link to comment Share on other sites More sharing options...
Pegasus Posted February 7, 2003 Report Share Posted February 7, 2003 HI Stephanie, There's a great many post here on CO2 in the Technical Section, and you can also find some links in the "Useful Links" at the top of this section also. If you are into plants, then clicking on the "Twin Fishes" at the top of the page will take you to another area of the forum where there is a plant survey and other great stuff. Regards, Bill (Pegasus) Quote Link to comment Share on other sites More sharing options...
stemar Posted February 7, 2003 Author Report Share Posted February 7, 2003 Hi, I am not talking about building a CO2 injection system (of which there are many posts) rather I am talking about building an electronic controller that will measure the pH and adjust CO2 injection to either raise or lower pH thereby controlling pH at a set value. Stephanie Quote Link to comment Share on other sites More sharing options...
john1 Posted February 7, 2003 Report Share Posted February 7, 2003 Hi stemar Electronics is one of my hobbies. Building the controller itself is chickenfeed. Not very expensive either. But, the pH probe to suit is very expensive. Because of the complexity of the probe, the project is not really viable. The controller can switch 10 tanks on and off, check the temperature etc. etc. All cheap. But NOT the pH part. Making a redox (conductivity) reading is also reasonable cheap. You can think of dozens of thing you can do with a microprocessor, but forget the pH part. John Quote Link to comment Share on other sites More sharing options...
stemar Posted February 7, 2003 Author Report Share Posted February 7, 2003 Hi John, Hey sounds great. Have you actually built one of these controllers? I am not interested in building a pH probe (always thought that I would buy that part - as you say to hard) just the electronic controller. Stephanie Quote Link to comment Share on other sites More sharing options...
john1 Posted February 7, 2003 Report Share Posted February 7, 2003 Hi stemar Yes, I have build a controller. But a controller is a controller. That's what the name stands for, controlling things. Sprinkler, garagedoor etc. But maybe I did not express myself sufficiently. The pH probe has to be read by the controller. And that is the hard part. Because of the high immunity and stray noise. Electrical noise that is. If you want to measure the conductivity, temperature, waterlevel or filterpressure, thats easily done. But NOT the pH. Thats a complete different thing. John Quote Link to comment Share on other sites More sharing options...
stemar Posted February 7, 2003 Author Report Share Posted February 7, 2003 Hi John, Sorry for the misunderstanding. "The Krib" article provides enough schematics (sort of, with a few modifications) to actually build a controller that takes input from a probe and then controls a solenoid to release CO2. This is what interested me about the article - building something that most people think is too hard. So depending on the availability and price of parts I think I will give it a go. It maybe that I am unable to get the accuracy of reading required (if at all) - if it works great I have done something that not many people seem to try, if not at least I tried. Thanks for all your help and advise. Stephanie Quote Link to comment Share on other sites More sharing options...
john1 Posted February 8, 2003 Report Share Posted February 8, 2003 HI Stephanie When you have the time, could you send me the link from the krib pertaining to that article/schematic Thanks John Quote Link to comment Share on other sites More sharing options...
stemar Posted February 8, 2003 Author Report Share Posted February 8, 2003 Hi, It was with my original post. Here it is again. http://www.thekrib.com/Plants/CO2/hurley-co2.html Stephanie Quote Link to comment Share on other sites More sharing options...
john1 Posted February 8, 2003 Report Share Posted February 8, 2003 Hi Stephanie. The project is about 10 years old. I'll see if it can be computerized. That is use a microchip instead of all the discreet components. Will stay in touch. John Quote Link to comment Share on other sites More sharing options...
stemar Posted February 8, 2003 Author Report Share Posted February 8, 2003 Hi John, Having already spent a fair amount of time on this idea, I believe I have a working solution - especially after todays research. Thanks for the offer of assistance. However I feel that I am in a better position to develop my own solution for my own requirements. All the best on your own research and development. Stephanie Quote Link to comment Share on other sites More sharing options...
Warren Posted February 9, 2003 Report Share Posted February 9, 2003 If you are worried about electrical noise as mentioned by John, it is a simple procedure to replace the first two op-amp stages with a precision instrumentation op-amp. These devices have programmable gain and offset adjustment. Both the Gain and Offset are temperature stabilised also. They are a little pricey, but are worth it. The differential input stage if designed correctly will allow enough common-mode range to stop any noise effecting the reading. There is also no low-pass filter section to remove any high frequency noise. There is an optional cap 'You may need a cap here, I didn't' that is supposed to serve as a low pass filter, but is more likely to make the output of the opamp unstable to high frequencies. While the circuit is fairly good for how basic it is, there are many improvement that could be made to make it more temperature stable and have less drift as it ages. Also, to use CO2 injection with pH controllers controlling the CO2 delivery you must have the correct KH. The KH/CO2 balance is what sets the pH in this type of setup. If your KH drops then the controller will put in less CO2. If the KH goes up (maybe during water change) then more CO2 will be added to pull the pH down. It is possible to add too much CO2 if the KH is unstable. pH probes usually need regular cleaning when used permanently in aquariums. Proteins stick to the probe slowy making the reading go up and therefore the CO2 go up. If the probe gets too blocked with protien, you can poison (suffocate) all your fish with CO2. After cleaning it may take several hours for the pH probe to stabilise back to the correct reading. I looked seriously at pH controlled CO2 but decided against it due to the risk involved. I didn't want to lose all my Discus due to a controller / probe stuff-up. I use a timer controlled solenoid, needle valve and gas reactor in the filter return. It has been working fine for over 6 years now and has never once missed a beat. It never needs maintenance (except filling the CO2) . You also don't have to worry about the KH or pH. The pH fluctuates less than 0.25 in a 24 hour cycle so is ok. The CO2 is added in sufficient quantity to make the plant grow really well. If you insist on an automatic system, don't skim on anything. Use the best temperature and age stabilised components you can get (both op-amps and voltage references). Find a really good quality probe (it will cost $200-250 for a good one). Quote Link to comment Share on other sites More sharing options...
john1 Posted February 9, 2003 Report Share Posted February 9, 2003 HI Warren The last paragraph is 100% correct. It needs a good quality probe plus the amplifier has to be a highprecision one. Not cheap. Furthermore the LF557 is not available anymore. The circuit is over 10 years old. But with dKH I don't agree 100%. Yes, the dKH has to be higher than 4°, but I would have that with or without a pH controller to begin with. Better stability. And you are right, a stuffup or malfunction can kill all the fish if the amount of Co2 exceeds the amount required. But taken 2 units side by side, one non-controlled, the other controlled. Both can kill if one is not vigilant. The only problem with an automatic system, one becomes complacent. But if both systems are watched, by way of an Co2 indicator, like the DAUER Test then all should be ok. John Quote Link to comment Share on other sites More sharing options...
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