pH/CO2/kH chart

Because you're not adding CO2

Just changing the distance between KH and pH doesn't give you more CO2. All you are doing is buffering the KH up, and you aren't using CO2 to do that.

The only way to get CO2 into your tank is to inject it in some form.

Roan

You can't increase kH without inevitably increasing pH. You're at 6.8 now, but you won't be after you increase hardness.

Pssst . . . for what it's worth, I wondered the same thing when I started. I mean, why not? Made sense to me!

Roan

I think I even had a thread based on the same assumption.

I've also learned not only does PH rise along with KH but that anything that shows over 5 ppm of CO2 without injection is caused by phosphate buffers in the water.

Water can only naturally hold 5 ppm of CO2, anything else is a false reading. Unless its injected.

What if a co2 test is revealing much higher levels of co2 than what that chart says? I tried using that chart after learning to pay attention to KH but my co2 test never jives with it. I tested my non injected tanks and tap water and they all read high on my co2 test. Is it possible I have wasted my money on this test kit?

Most test kits are not all that accurate. I was testing pH and it was 6.8, pretty consistently. Then I bought another brand of kit (on sale!) and it said 7.0 -- so I picked up a pH standard solution of 7.000 and ran both tests -- my pH was 7.0 not 6.8. This kicked my CO2 down 10ppm or so out of the good range into the too-low range. I don't know about my kh test -- I suspect it is a bit more accurate just because of how those tests work. So if I now believe my pH and kh I have to raise my CO2.

I read somewhere on a lamotte (lamotte tests being the best and very!! expensive) that co2 testing is inherently difficult and inaccurate and that using pH and kh is simpler -- but to use that you must not use other things to change your pH,
specifically do not add acid or base (ph-down/up products) to change your ph. It also
assumes that you don't have an overabundence of some types of buffering agents,
I don't remember the details -- but I gather than most waters are OK with the
pH/kh method. But as I said at the start, pH test kits tend to be pretty inaccurate
so you might pick up a standard 7.000 solution and test your test.

quenton said:

Most test kits are not all that accurate. I was testing pH and it was 6.8, pretty consistently. Then I bought another brand of kit (on sale!) and it said 7.0 -- so I picked up a pH standard solution of 7.000 and ran both tests -- my pH was 7.0 not 6.8. This kicked my CO2 down 10ppm or so out of the good range into the too-low range.

Click to expand...

A .2 difference I can prettymuch live with as I personally can't judge the colors to within .2 anyways. Depends on the lighting of the room...etc., all seem to shade the color just a little bit different, I consider an accuracy of .2 to be pretty good on a ph scale just for measurment. However I am talking about much larger differences. What I originaly posted was in regards to my CO2 reading over 60ppm while the chart was showing number in the teens. I tested my tap and my guppy/plant tank and if I remember correctly they were both testing near 30ppm. I know cold water can contain more co2 but it just seems as though my test kit is reading too high. When I first got it, about 6 months ago, it seems like it was right in the ball park - typicaly reading teens. I'll have to restest for phosphates but the last time they were high my algae went nuts so I am thinking they arent very high right now. The only other thing I have been adding to the tank besides co2 and baking soda is Kent Freshwater Plant 0-0-3 "contains no phosphates".