Morning Fishy: I've got some figures for you.

Water pH is 6.5
Water KH is 2 (35.8 ppm)

Using the Calculation you provided:

CO2 = 3 x 2 x 10 ^ (7 - 6.5) = 18.97 ppm.

That falls nicely in the Green zone, on that chart, between 10 and 25 ppm. One thing that has me puzzled, is that I've failed to detect a pH swing between Evening and Morning. The pH reading at lights out, and Lights on, is 6.5. My Tap supply is 6.7. I suspect a dodgy Fermenter batch, I can't actually see my Bubble Maze for the Plants! My Breeding Tank, without CO2, is also at pH 6.5.

Although I did expect the Tap would be higher than the Tank, I'm surprised that it's not up around 7 - 7.1. I guess the Reservoir being under 50% for a few years has had some effect. My last Tap reading was before the drought, at pH 7.2.

I guess I need to check out the Fermenter, and run all my test's again... This is fun, isn't it?

i have to say i am slightly surprised by the results based on what u've told me already. i was realy expecting ur co2 reading to be lower.

i can only think of the possible following conclusions.

my 1st thought is that the readings could be wrong, not that u took them wrong but that the test kit/s, and more likely the ph test kit, is not giving the reading it should. i say this for 2 reasons. i once tried aquarium test strips for ph and found them very inacurate. they always read lower than they should have. the other reason may be if it is an old ph test kit, it may be faulty due to age. the probabilities are that the ph test kit is ok, but it might be worth checking if u can. if the kh test kit is new it should be accurate i imagine.

the second conclusion i can think of is that ur bubble maze is working better than i expected it to. if the readings are correct then u r getting a good amount of co2.

regarding ph swings, it may be that the swing is that small u r not able to detect it with the kit u r using. which is a good thing. i have a dropper ph test kit that is acturate to about +/- 0.3. i havent tested for a ph swing with this kit yet, but i also have an electronic ph tester acurate to about +/- 0.02. when i did test my ph for a swing ages ago with the electronic ph tester, the swing wasnt more than 0.3 ph. i havent tested it for ages tho with the electronic tester as it needs calibrating and i dont have ph buffer to calibrate it.

to sum up, i think either u r getting a good reading and ur co2 is fine, with a small ph swing or the ph test is wrong and probably reading lower than it should be, which would mean ur co2 is less than calculated and in line with my original guess.

only way to be sure would be to retest and maybe with a new ph test kit if the current one is old or test strips rather than a dropper test.

regarding ur kh, it would seem that ur water is soft but obviously does have a kh content unlike mine. a reading of 2 is the lower limit for a co2 added tank, from what i've read. most of what i read have recommended a reading of 3 or higher. saying that tho, the reason for having kh of 3 or more is to stop the ph swing. if u cant detect a ph swing, perhaps a kh reading of 2 is fine. if u wanted to raise the kh a bit u can do this easily by adding some bicarbonate of soda to the water changes at a rate of about 1gram to 10gals, at a guess.

if there are any changes or developements i'd be interested to know

You may remember that I asked the Aquarium Bloke what our water hardness is, and He said "40, and too soft". My KH reading of 2, equates to 35.8 ppm, so I figure that's close enough to be a valid reading. The KH kit has no expiry date.

My pH kit has an expiry of 2008. I do have an Electronic pH tester with a batch of pH buffer, I just have to find which box, in which cupboard, I've buried it. Perhaps I could utilise that to corroborate the chemical reading.

Certainly everything I've read, plus your own thoughts, has led me to believe there should be some swing. Maybe my low CO2 dosing rate has something to do with it? I know you can't trust the Sales Pitch, but my 'destructions' do state that a tank my size, should have two fermenters.

In any case, I'm loathe to start playing with chemical additives (other than CO2).