Estimating CO2 levels.

[tug]

When I used DIY CO2 I just assumed I was providing low levels of CO2 so I never spent a lot of time trying to measure it.

Now, I am using a pressurized CO2 setup and try to maintain between 30 & 40ppm of CO2 during the day. Without testing for KH, water taken from the tank, sits for over 24hrs, has a pH of 7.6 and in the tank, just before CO2 comes on, the pH is between 7.6 & 7.2 according to the API test kit and my eyeball. After CO2 is added and just before the lights go on, pH is ~ 6.6 and at days end I am reading ~ 6.4pH.

• 
• Does this drop in pH tell me anything without knowing my exact KH?
• What happens when CO2 levels climb, increasing from 3 to 30-45ppm?

The water quality report for DC shows alkalinity on average at 64ppm (I think that's 3.5 dKH).

DC Water Quality Test Results
http://www.dcwater.com/waterquality/test_results.cfm

Reason for edit: semantics

[JLW]

Without knowing your KH, you really can't tell much.

But, look at your plants. Are they pearling? If so, you have more than enough CO2. If not, you can probably increase it.

Anyone ever see the Simpsons episode where Homer wants a lobster, finds out how expensive they are, and decides to buy the smallest one and grow it up? He plonks it in a tank with goldfish, and the lobster starts floating. "DAD! Lobsters are saltwater!" screams Lisa. He dumps salt in, and the goldfish float upside down, lobster right side up, so he adds water until they're both not-dead. Sometimes, I feel like this with CO2. Add CO2 until your fish start to die and the plants are doing well, then back it off just a lil' . . . . .

[tug]

The pH/KH/CO2 table will never replace watching fish and plants, the tried and true method to our madness. That is because CO2 levels are not linear as the pH drops and why at higher concentrations (the lower the pH) a small drop in pH can be devastating.

Another reason is because KH readings are not always accurate - KH may not be entirely carbonate hardness. If the water is high in phosphates or there are other buffers, values for CO2 based on pH and KH can lead us to believe there are high levels of CO2, when in truth we are under dosing CO2. This is more commonly a problem in water with a KH of 4-5 and above.

I asked these questions because I truly didn't know. I had read about estimating CO2 levels using pH alone as a guide, that a one degree drop in pH might provide another way to estimate CO2 levels. It should be a more accurate indicator then the pH/KH/CO2 chart. Here is how and why I think it would work.

The pH drop is relative to ambient CO2 levels of about 2-3ppm, for any KH value. From there a pH drop of 1.0- to 1.3 would correspond to a CO2 level around 30-45 ppm on the chart.

That would be independent of KH.

We can test this using any CO2 enriched tank. Test the pH from the tap after it sits for 24 hours and later, in the tank, when CO2 levels are at there lowest.

[fredyk]

I like a drop checker. Without being scientific about it, when the water in the drop checker changes from blue, that's ok, and green is good.

Referencing JLW above, CO2 is a poison at high concentrations, which I know from experience.

[tug]

One reason CO2 can turn deadly so quickly when relying on pH as a guide is it gradually increases as the pH drops until it reaches levels above 20 ppm, when drop checkers start to turn green. Using a kH of 4, on the chart, start with an ambient CO2 level of 2-3 ppm. A drop in pH of 0.4 degrees equals an increase in CO2 levels of around 3.5 ppm - a gradual increase over a period of maybe an hour. What happens when the CO2 levels start to reach 20ppm? A 0.4 degree drop in pH can mean an increase in CO2 levels of about 27ppm. The drop checker is still green and this problem is compounded by the possible lag in time it takes a DC to provide an accurate reading - as much as an hour or more.

Another problem I find with pH readings in general is trying to tell the difference between the shades of green. The drop checker is a good example. If perfectly green, the CO2 level is 30 ppm. When I look at green in a drop checker it could be +/- 0.2 degrees pH, between 19 and 47 ppm CO2. That's a large margin for error. Trying to tell the difference in green from a drop in pH in my tank, using an API test kit, I have a similar problem but the results are in real time and I can watch the progression more closely.

One way around the problem of using a drop checker is to use two drop checkers. Any one know the joke,
what's better then one roll of duct tape? Hoppy writes up some neat information on Drop Checkers at The Planted Tank.
http://www.plantedtank.net/forums/showt ... p?t=129720

To make a reference KH for colors green or yellow,
click on the link to "drop checkers" at the top of Wet's calculator to make easy work of the math.
http://rota.la

[fredyk]

What does Plantbrain think (cause he's pretty smart)?

Pertaining to the joke, is the answer like the following: second prize 2 weeks in philadelphia; 1st prize 1 week in philadelphia? (disclaimer: philly suburbs=my hometown)

It seems to me, without thinking about it, if the drop check changes color somewhat, then you have more CO2 than you started with.
I have killed too many fish with CO2; it scares me.

[tug]

If you mean ask Dr. Barr, a.k.a., plantbrain - he isn't a big proponent of drop checkers. If you use a 4dKH solution, the color changes to a blue-green at around 19ppm, then to green-green around 30 ppm, and to a green-yellow when CO2 levels have reached 47 ppm. IME, not a bad guide really, if you can live with the delayed response. I've used them but got tired of fishing them off the bottom of the tank after their suction cup lets go of the glass. Now, I find it's easier to check my pH and keep an eye on the fish.

IMO, this is basically what people who use a regulator with a pH controller do, set the controller to shut down CO2 when the pH drops to set point, using the pH/KH/CO2 table to determine the pH.

I'm saying, to dial it in closer, check the pH of a water sample after it gases off CO2 for 24 hours and compare it to the drop in pH, in the tank, later in the day. If it is less then a 1-1.3 degree drop and the pH controller shut off the CO2, make an adjustment to tune it in further but carefully adjust from there. I would be interested in hearing from anyone, particularly if they have experience using a pH controller, if they have tried testing the drop in there pH relative to ambient CO2.

Keeping CO2 enriched tanks is a daunting task. The equipment alone is scary and any test for CO2 levels is fraught with possible errors. That's why I had a hard time using anything other then yeast. CO2 regulators and their potential, is intimidating.

Keeping CO2 levels around 20 ppm, providing mid-levels of light and growing easy plants is not as fearsome and has a lot going for it. Some people might do nothing to measure CO2 other then watch their plants/fish and they have successful tanks under a wide range of conditions and lighting levels. They probably have a lot of experience under their belt. Others don't measure CO2 and kill fish. Others think they are deficient in Ca, or K, claim their Mg levels are too high or declare phosphate levels are out of balance - when CO2 and light are hardly given the attention they deserve. The more we know, the less frightening and ambiguous CO2 enriched tanks become, the more we can help each other. That's all.

Pertaining to the joke, is the answer like the following: second prize 2 weeks in philadelphia; 1st prize 1 week in philadelphia? (disclaimer: philly suburbs=my hometown)

If you know the answer, you get a red neck like mine.

[JLW]

Blah blah blah blah blah blah, look at your plants.

[tug]

Joshua,
I'm trying to understand how different methods for estimating CO2 work and how accurate they are - not if they're necessary. Understanding their accuracy, limitations, how they can be used properly and personal experience can sort out if or when they can be useful. Just having a tool in my tool box I use once in a blue moon, doesn't make it any less effective.

I have plants pearling (some of them any way) and I am keeping an eye on my fish. I would like to explain/understand how watching plants works but don't have enough experience, bailando con los terroristas. Sean gave an excellent talk explaining it at our last meeting.

[JLW]

I recommend drinking 3-4 Five Hour Energies and having a conversation with Sean about this. ;-P

I have no idea what my CO2 level is in my tank. And I don't care. The plants grow well, the fishes are happy, what more can I want? But, Ic an understand why you might want to know.