My JBL CO2 m603

[Leowalton]

I wondered if anyone could help me.I recently set up a planted aquarium and am having problems setting up my JBL m603.I have changed the original reactor that came with the setup for a glass diffuser. I carried out the calibration,set the desired PH level and measured and entered the KH which is 9 in my aquarium water. My problem is that I hardly see any CO2 being diffused through the ceramic plate in the glass diffuser into the aquarium. Whenever I have seen other people using the same setup there seems to be CO2 being almost constantly diffused!
Please help,what am I doing wrong!

 

[ceg4048]

Hi,
Please define "desired pH level", and advise what the current pH level of the tank is.

Incidentally, it's not really a good idea to use the pH controller to control the CO2 levels unless you set the commanded pH to a very low level, such as 6.0 or so.

Cheers,

 

[Leowalton]

Thanks for taking the time to write.I set the KH level on the computer as 9 (which I tested with Kh kit)and set the Ph to auto and it is showing about 6.92 from the electrode.

 

[ceg4048]

Well it's really not clear what the commanded pH will be in AUTO. If you're going to use the pH controller to drive CO2 injection you had better have a good idea as to what pH you want to command to.

PH controllers are easily fooled because they cannot determine the source of the acidity in the tank. Tanks contain nitric acid, ascetic acid, phosphoric acid and others as well, all which affect the pH. Carbonic acid is produce when you inject CO2. So the probe can only report what the acidity is. It cannot tell you how much of the ph is derived from carbonic acid as opposed to the other acids in the tank. You have to tell the controller what pH set point you want. You have to drive a pH value low enough that most of the acidity is caused by the carbonic acid. If you have a 6.9 pH with no gas being injected then set a pH of 6.6 so that the valve opens and CO2 will be injected.

The controller assumes the standard ph/KH/CO2 relationship equation;

CO2 (in PPM) = 3 * dKH * 10^( 7-pH )

But as I said, the flaw in this is that the pH value in that equation must be derived ONLY from carbonic acid. Ordinarily, when you look at the charts or if you use the equation directly from the parameters of your water, you would get numbers like this:

CO2 in PPM = 3 * 9 * 10^( 7-6.92 )
CO2 in PPM = 27 * 10^.08
CO2 in PPM = 27 * 1.20
CO2 in PPM = 32.4 PPM

So without injecting any CO2 at all the computer thinks that you have sufficient CO2 because the recommended CO2 concentration level is 30 ppm. That's because the 6.92 pH reading is corrupted by other acids in the tank. That is THE flaw of a controller.

Knowing that the CO2 ppm is closer to zero than 32.4 you just need to select a pH that will generate a DIFFERENCE of 30ppm from what it computes currently. Using a commanded pH of 6.6 now gives the result:

CO2 in PPM = 3 * 9 * 10^( 7-6.6 )
CO2 in PPM = 3 * 9 * 10^( 0.4)
CO2 in PPM = 67.82

This more or less will give you the difference (67.82 - 32.4) of 35 PPM.

Again, this is not a guarantee either because acids are produced in the tank constantly, so the true component of carbonic acid is never really known. This often causes the the controller to vary the CO2 injection and can trigger some forms of algae, BBA is the most prominent. You have to therefore outsmart your own computer to get it right. You would be better off setting a constant injection rate and just use the electrode to tell you what the pH is in the tank.


I assume there are no fish in the tank, right?

Cheers,

 

[Leowalton]

My goodness,I feel guilty having taken up so much of your time.There are a few otocinclus' in the tank but I haven't stocked it yet as I want to sort this CO2 dosing first. Thankyou for taking the time to respond.I am having certain regrets at not having got a standard kit with a solenoid valve for the night. I am going to try and outsmart the ph computer later,fingers crossed! Thanks again!