PH set point? - The Planted Tank Forum
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post #1 of 19 (permalink) Old 03-10-2016, 02:10 PM Thread Starter
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PH set point?

What PH do you set your PH controller to run at with automated CO2 injection? I have mine currently set at 7.0 and am using a 50% blend of RO and tap until I get a RO unit for the house. Not sure what my GH is as I haven't tested it yet, thanks.
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post #2 of 19 (permalink) Old 03-10-2016, 02:26 PM
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I can tell you what I'm doing. As a newbie to this sport, take it for what it's worth.

- test your Kh, and determine if that number is where your tank will likely run
- refer this chart to find your desired pH to get the CO2 level where you want it (30 ppm is common)
- set your controller to turn on CO2 when it's .05 pH higher than your goal, and to turn off when it's .05 below your target pH
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Last edited by Ben Diss; 03-11-2016 at 01:23 AM. Reason: Fixed 3rd point on pH setting, changed .5 to .05
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post #3 of 19 (permalink) Old 03-10-2016, 02:29 PM Thread Starter
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Thanks Ben, I need to test my hardness and go from there.
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post #4 of 19 (permalink) Old 03-10-2016, 03:45 PM
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Quote:
Originally Posted by Ben Diss View Post
I can tell you what I'm doing. As a newbie to this sport, take it for what it's worth.
- test your Kh, and determine if that number is where your tank will likely run
- refer this chart to find your desired pH to get the CO2 level where you want it (30 ppm is common)
- set your controller to turn on CO2 when it's .5 pH higher than your goal, and to turn off when it's .5 below your target pH
Couple comments:
  1. You do not want to have that big of a range in your pH set point; if, for example, you have a target pH of 6.5 at a kH of 3 (29 ppm, which is reasonable), letting your pH get to 6.0 before turning it off and not turning it on until it gets to 7.0 is a swing from 9 ppm to 90 ppm of CO2. This is not good. Beyond the fact that 90 ppm is going to be very hard on your fish, large swings like that are an invitation to algae problems.
  2. Using the kH method to calculate CO2 concentration by pH is only accurate if sodium bicarbonate (I think) is the only source of carbonate hardness, but most of the time there are other sources, so using this method will usually result in a little bit less CO2 concentration than you think you are getting.

In addition to using the kH method, I also have a drop checker and check that I am only dropping the pH by about 1.0 (from no CO2 to target point) between the three methods, I am reasonably sure that Im pretty close to 30 ppm. Also, my pH controller is set to turn on at 6.6 and off 6.65 - not that I'm saying that's the target you should use, but I would keep the range from on to off closer to the 0.05 to 0.1 range.

-Justin
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post #5 of 19 (permalink) Old 03-10-2016, 03:54 PM Thread Starter
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I currently have my controller set for 7.0 so CO2 only comes on if PH goes above that.
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post #6 of 19 (permalink) Old 03-10-2016, 07:00 PM
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I might mention several points for you to review and consider how they fit you. I find fish are far better if changes are made VERY slow and gentle. That makes me add CO2 very slowly and increase over an extended period like weeks rather than suddenly. I use a Milwaukee controller which makes it very simple to read the PH and set it a couple tenths lower and then gradually move it lower as I let the fish adapt and see what they can tolerate. Some fish adapt quicker and some more than others so I use them rather than any theoretical number.

Second thought is the chart. I found using the chart and testing was totally useless for my water. I have very hard, very alkaline water.(PH 7.8+GH above 300) The local water runs in limestone most of the time before hitting the tap. The charts would have me believe I was running 80 PPM of CO2 so I no longer use the chart. To use the chart your water has to have a very specific makeup which is often not the case for much tap water. Throw in some other chemical makeup, some lack of precision in testing and the charts can get way, way off base.
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post #7 of 19 (permalink) Old 03-11-2016, 12:10 AM Thread Starter
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Thanks for the input Rich, just got back with test kits and my KH is 7 and my GH is 179. If the chart is or was correct at 7.0 I would be right in the middle of the green zone. Since this is my first HT plant tank think I will let it ride where its at and start slowly lowering my KH with RO water changes. I have cardinal tetras so if anything gets whacky they will surely let me know!
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post #8 of 19 (permalink) Old 03-11-2016, 01:21 AM
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Quote:
Originally Posted by jrygel View Post
Couple comments:
  1. You do not want to have that big of a range in your pH set point; if, for example, you have a target pH of 6.5 at a kH of 3 (29 ppm, which is reasonable), letting your pH get to 6.0 before turning it off and not turning it on until it gets to 7.0 is a swing from 9 ppm to 90 ppm of CO2. This is not good. Beyond the fact that 90 ppm is going to be very hard on your fish, large swings like that are an invitation to algae problems.
  2. Using the kH method to calculate CO2 concentration by pH is only accurate if sodium bicarbonate (I think) is the only source of carbonate hardness, but most of the time there are other sources, so using this method will usually result in a little bit less CO2 concentration than you think you are getting.

In addition to using the kH method, I also have a drop checker and check that I am only dropping the pH by about 1.0 (from no CO2 to target point) between the three methods, I am reasonably sure that Im pretty close to 30 ppm. Also, my pH controller is set to turn on at 6.6 and off 6.65 - not that I'm saying that's the target you should use, but I would keep the range from on to off closer to the 0.05 to 0.1 range.

-Justin
Thank you. I fixed a typo in my post. I run my pH from 6.8-6.9.

I also read the post here that pointed out the error in the CO2 calculation using KH and pH. My drop checker looks good, so I think it's working, but I agree this method isn't completely accurate.
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post #9 of 19 (permalink) Old 03-11-2016, 01:56 AM
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Very generally, a full 1pH drop = 30ppm CO2. Forget the KH/pH/CO2 table.. I've also found it to be incorrect given the confounding variables in each setup.

What's your pH before injecting CO2? As an example, If it's 7.5pH you'd want the controller to maintain 6.5pH.

The 1pH drop method isn't perfect either, so make sure you keep a close eye on livestock to note any issues early. Add a strong airstone to gas off excess CO2 if necessary, then reduce CO2 injection until livestock are comfortable and algae and plant growth are ok.
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post #10 of 19 (permalink) Old 03-11-2016, 02:11 AM
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Crank it up slowly over a few days or a week, until the fish show signs of distress. Then back it down to where they are comfortable again. Set PH to whatever that is.


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post #11 of 19 (permalink) Old 03-11-2016, 06:11 AM
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Crank it up slowly over a few days or a week, until the fish show signs of distress. Then back it down to where they are comfortable again. Set PH to whatever that is.
This is the best way to calibrate your CO2. Should take 1-2 weeks to properly dial it in.


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post #12 of 19 (permalink) Old 03-12-2016, 02:36 AM
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I agree, skip the chart. Take a small sample of tank water in a jar and run an airstone in it for 30 minutes. Test the PH preferably with a PH pen as it is much more accurate than test tube kits. This is the PH with no co2, or de-gassed PH. Then set the controller for a .8 drop. For instance if your de-gassed PH is 7.6 then set the controller for 6.8 and slowly over days adjust from there.

A .8 drop gives you a big safety margin to start with. I am currently using a 1.2 drop and my fish are fine but you need to go slow. After your .8 starting point never make adjustments unless you are going to be there for a few hours to observe the fish.
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post #13 of 19 (permalink) Old 03-12-2016, 05:29 AM
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Since the tank water as the fish have it is what matters to me, I don't bother with testing other than the tank PH when setting the controller. I normally find something like 7.8 so set the controller for that for a day or so. Then as I see all the bells and whistles are turning on and off as expected, I begin to move the set point down at about .2 per adjustment and give at least a day to see how it fits. For my 75 tank of Central American cichlids, I got it down to 6.8 with no complaints from the fish but when working my 125 of African cichlids they began to get sort of groggy acting at less than a full 1.0 drop and stopped when they said. Some acted far more effected than others but over a few months I ddi work it down to the full point drop as suggested without any fish troubles.
Since I was sure it would take time for the plants to change and show progress, I saw no reason to rush the CO2 changes as it was just a matter of turning the knob a tiny bit each time. But then since all water differs slightly, each tank differs in stocking, feeding and care, it seems very natural to expect CO2 to work slightly different in each of our tanks.
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post #14 of 19 (permalink) Old 03-12-2016, 05:36 AM
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I've found quicker growing plants take 1-2 weeks to show confirmable change due to CO2 adjustments. Slow growers take longer and the time frame can vary greatly.

Algae takes just days to show change due to CO2 adjustment, and for me this is the best short-term indicator.

I think you'd be safe to aim for a 0.5 drop with the controller. Just make sure you're home for the day to monitor livestock.
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post #15 of 19 (permalink) Old 03-12-2016, 01:42 PM
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..
Algae takes just days to show change due to CO2 adjustment, and for me this is the best short-term indicator...
That could be true in a well planted tank, but if the tank isn't well planted co2 effect on algae woulld not really be noticeable.
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