Estimating CO2 levels - Page 2 - The Planted Tank Forum
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post #16 of 40 (permalink) Old 04-17-2020, 05:08 PM Thread Starter
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Originally Posted by Quagulator View Post
Could you point me in the direction of these experiments? I myself would like to better understand this for future use. Many times we see these tests / experiment being perform in a completely different scenario than aquariums, and little can be brought over to our world of fish tanks without massive assumptions.

Again, could you elaborate on this a little more? Every tank here that uses pH drop is getting 30-40ppm at a drop of 1.0 - 1.4. Of course it's not the same on every tank that's why I stated:

Well, I guess some waste is necessary, unfortunately.
?
What experiments? I'm referring to a mathematical formula which as far as I know hasn't been seriously questioned and with no exceptions for aquariums or anything else. It is what it is. I don't see the experiments showing it doesn't apply to aquariums.
Wrt your "30-40 ppm" statement (which is not supported by the science or math) I would ask the same back at you: can you show experimentation or real data to back that up? I've seen that all over but no one ever cites scientific proof. It seems more like a legend passed down through the aquarium ages.
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post #17 of 40 (permalink) Old 04-17-2020, 05:44 PM
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The 1 point drop = 30 is supported by math. But you have to assume a baseline around 3 ppm, which is what most degassed or non-injected tank will have.

When you take that as the starting point, dropping 1 point from that yields about 30 PPM, regardless of the KH.

Starting point: 3 PPM CO2.

pH 6.76, KH 0.5 = CO2 3.06
pH 5.76, KH 0.5 = CO2 30.61

pH 8.1, KH 11= CO2 3.08
pH 7.1, KH 11 = CO2 30.78


Starting point: 3.5 PPM CO2.

pH 6.7, KH 0.5 = CO2 3.5
pH 5.7, KH 0.5 = CO2 35.14

pH 8.04, KH 11= CO2 3.5
pH 7.04, KH 11 = CO2 35.34

Calculator - Paul's Aquarium Page
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post #18 of 40 (permalink) Old 04-17-2020, 06:14 PM
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This is the formula I was looking at a while back:

CO2ppm = 3 x dkH x 10^(7.0 - Tank pH)

Ex: kH of 4, pH of 7.6 and a pH drop from CO2 of 1.0:

3 x 4 x 10 ^ (7.0 - 6.6) = 12 x 10^0.4 = 30ppm CO2

Now, same scenario but with: kH of 12, pH of 8.0 and a pH drop from CO2 of 1.0:

3 x 12 x 10 ^ (7.0 - 7.0) = 36 x 10^0.0 = 36ppm CO2


Does this seem accurate or did I find a bad formula?
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post #19 of 40 (permalink) Old 04-17-2020, 08:30 PM Thread Starter
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Ok. I really appreciate the replies and apologize if I sound argumentative. Just trying to sort out this subject in my mind as it's relatively new to me, although I've kept planted aquariums for a couple years now. It was just recently when I found my plants were really not doing well which coincided with a friend gifting me a CO2 setup, that I started to take a closer look at this stuff. I'm not chemically inclined, nor mathematically, but I can sort out information to get to the bottom of what I need.

Tap water:
- Well water, via water softener and GE Whole House filter
- ~78F
- dKH = 14
- GH = 12
- Last water change 30% 7 days ago

Tank water:
- 78.5F
- dKH = 15
- GH = 17
- pH = 7.0

This 65 gallon tank has an AC110 HOB running 24x7 and two sponge filters that only run a couple hours a day. It also has a ~3" substrate of 3:1 baked clay (Oil-Dri) and Eco Complete, with a 3/4 inch plenum with Bio balls. It's 19 months old. I've recently dropped in a "Wonder Shell" because I was concerned about the appearance of my Nerites' shells. Plants are fed with Easy-Green and Flourish twice a week as prescribed.

My take-away from this discussion are:
1. Both the chart and the formula behind it, and the formula cited on Paul's page (which I wasn't aware of, thanks burr740!) show negligible differences in my case. The chart says I have ~42ppm CO2 and by Paul's it's 48ppm. That's a trivial difference so that's good (with the caveat that both have their flaws). In either case I would benefit from lowering my hardness to decrease CO2 usage as well as setting the pH controller to something more like 7.4. I'm changing the pH first as that's the easiest.

pauld738, I had seen that discussion, and many others. Thank you. It does go deep into the weeds for my brain but still useful.

Again, I'm not trying to pinpoint the level of CO2 saturation. I know that's hopeless. I just want to do better than dumping it in and hoping for the best. Having two scientific sources to guesstimate that appear to jibe is more than I had before since I came into this with the notion that the chart was too flawed by itself.

Thanks again, and I look forward to the day when all we need to do is look at a gauge to tell us CO2 ppm.
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post #20 of 40 (permalink) Old 04-17-2020, 08:31 PM
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Trying to figure out absolute values is a waste of time and will drive one crazy. And that goes for about everything that we do with a planted tank.

My PAR measures at 127 at the substrate. Is that the absolute value? Makes no difference. I do know that I can control relative the measured value, and I know what happens at relative values, like 100 PAR or 150+ PAR. That's all that matters.

I dose 15 ppm weekly NO3 into my tank. The theoretical max value is 30 ppm at 50% water change. Can I tell the difference between 25 ppm/30 ppm/ 35 ppm with test kit? No. But again, absolute value matters little. Regardless of the reading of the relative value, all that I can control is how much I dose. Again all that matters.

And the same goes for CO2. For our purposes, relative pH drop is all we can control. And dialing that in for the both fish and plants what is matters. According to the "charts' and math my CO2 concentration is about 100 ppm. Is that my real absolute value? Who cares, it's where the tank does the best.

Now all that being said, it would be interesting to know the absolute value. But the question is does anyone know of a completely reliable CO2 measuring device that would provide an absolute value in an aquarium? If it exists, I have not seen it.....but who knows if someone were willing to invest enough maybe there is one??

In the end, the proof is the state of the tank. I know the tanks very well of those posting in this thread, and their success has been demonstrated over and over.

@ChuckM any pics of your tank? And how do you think it would improve if you knew the absolute value of CO2 ppm??
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post #21 of 40 (permalink) Old 04-17-2020, 09:36 PM Thread Starter
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Originally Posted by Greggz View Post
Trying to figure out absolute values is a waste of time and will drive one crazy. And that goes for about everything that we do with a planted tank.

@ChuckM any pics of your tank? And how do you think it would improve if you knew the absolute value of CO2 ppm??

Well, yes and I said as much. And this isn't intended to be a t-shooting session and I'm not trying to pinpoint my CO2 saturation. I'm pretty satisfied with how things are going afa the health of the tank is concerned. But also, as I said, I came into this without a clear sense for how much CO2 I was actually injecting and given the questions around the accuracy of the KH/pH chart I am hoping to optimize my CO2 usage. It's a 15 mile drive one way to get my cylinder refilled and it costs $30 bucks each time. I'd really like to know I'm getting the most of each refill so I want to get a handle on efficiency. I've gone through two refills in the past two months and that seems excessive (and I've checked for leaks with soapy water). Maybe I'm using more than I need to so as a result of this discussion I'm dialing it back a bit.
I'm also a retired IT guy who's professional life for 24 years revolved around data and metrics. That doesn't apply so much to aquariums or other living systems but that's where I come from.
I may try to post a picture later but I don't think it's pertinent.
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post #22 of 40 (permalink) Old 04-17-2020, 09:48 PM
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It's a 15 mile drive one way to get my cylinder refilled and it costs $30 bucks each time. I'd really like to know I'm getting the most of each refill so I want to get a handle on efficiency..
Generally co2 is pretty cheap, so I never really worry that I'm getting the absolute best in terms of efficiency. How big is your tank and the cylinder your using that it has to be refilled every 2 month? As you probably know, using an HOB isn't usually the most efficient with air/water exchange and surface agitation.


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post #23 of 40 (permalink) Old 04-17-2020, 09:49 PM
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A 10 lb tank will last me about 10 weeks on a 75 gal. Ive gone through one in 5-6 weeks and also had it last 3 months. But at my current rate I get about 9-10 weeks out of a 10 lb.

Which is why I run 20 lb on all but one these days. The difference in filling a 10lb vs a 20lb is about $3 where I go. So I can fill a 20 lb 3x a year at $18 bucks a trip, or fill a 10lb 6x a year at $15 a trip. Financially you save a ton of money using the biggest tank you can.

Thats not even the biggest thing for me, I just hate taking the regulators off and making the trip then having to put it back together. And my place is a 30 min drive one way
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post #24 of 40 (permalink) Old 04-17-2020, 10:06 PM Thread Starter
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Originally Posted by Asteroid View Post
Generally co2 is pretty cheap, so I never really worry that I'm getting the absolute best in terms of efficiency. How big is your tank and the cylinder your using that it has to be refilled every 2 month? As you probably know, using an HOB isn't usually the most efficient with air/water exchange and surface agitation.

65 gallon tank, 20lb cylinder. 30 days per refill.
Yes, I'm aware of the inefficiencies of a diffuser but that's what I have for now.
$30 per refill at Airgas. I've called a local beverage center who wanted literally twice that.
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post #25 of 40 (permalink) Old 04-17-2020, 10:07 PM
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Well, yes and I said as much. And this isn't intended to be a t-shooting session and I'm not trying to pinpoint my CO2 saturation.
I wasn't trying to be argumentative, just making a point.........and in all fairness...................

Quote:
Originally Posted by ChuckM View Post
I think what I'm aiming for is to get an absolute value for the CO2.
So that is what I was responding to.

Quote:
Originally Posted by ChuckM View Post
It's a 15 mile drive one way to get my cylinder refilled and it costs $30 bucks each time. I'd really like to know I'm getting the most of each refill so I want to get a handle on efficiency. I've gone through two refills in the past two months and that seems excessive (and I've checked for leaks with soapy water)
But back to the matter at hand.

You are saying you are filling a 20lb tank once a month on a 65G tank?

If so, something is way, way off. I'm not sure what, but something is just not right for that size of tank.

For reference, I go through a 10 lb tank every 4 months with my 120G. High light, pH driven down 1.35 from degassed value. CO2 on for 8.5 hours per day.

Now my KH is less than 1.0. But back when my KH was in the teens it was about 10 weeks between fillings. So it does take more CO2 to drive down the pH of higher KH water relative to lower KH water. But I doubt tht has much to do with your situation. And the HOB filter could be a factor, but I do run pretty vigorous surface agitation all day long, so have quite a bit of off gassing as well.

I don't what is going on, or where to start other than looking for leaks again.......but like I said something seems to be way off. Maybe others have ideas??
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post #26 of 40 (permalink) Old 04-17-2020, 10:16 PM
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Quote:
Originally Posted by ChuckM View Post
65 gallon tank, 20lb cylinder. 30 days per refill.
Yes, I'm aware of the inefficiencies of a diffuser but that's what I have for now.
$30 per refill at Airgas. I've called a local beverage center who wanted literally twice that.
There's no way you should be burning through that much even with sub-optimal diffusion. Something is off somewhere. Do another leak check. Every single fitting on the reg and the tank and anywhere else you have a connection of any kind. Leaks are very easy to miss.

I have better luck using the bubble solution made for kids to play with. For me it works better than soapy water. Of course right now you may not be able to get that easily, just throwing it out there

Adding: To make the diffuser work better place it low in the tank on the opposite end of the main current. You want the current pushing the mist downward. it doesnt need to just rise freely to the top. Try to position it so that the mist gets blown around some. Lots of folks run diffusers on tanks that size, its certainly doable
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post #27 of 40 (permalink) Old 04-18-2020, 01:52 PM
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Some great suggestions above. Nothing to do with aquarium management but it might be worth weighing your bottle before and after filling and ensuring it is being filled properly. Just a thought.


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post #28 of 40 (permalink) Old 04-18-2020, 02:54 PM Thread Starter
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Yep. Frankly it hasn't been a priority since Airgas is a pretty well-established company in these parts for welding supply, etc.
But I will also be going over the rig today for leaks again, that seems to be the most likely issue.
Thanks.
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post #29 of 40 (permalink) Old 04-18-2020, 03:18 PM
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One time I had a leak and I couldn't figure it out. I ended up replacing the plastic O-ring on the cylinder with this and the leak stopped.

https://www.amazon.com/Leak-Stopper-.../dp/B018UNZLHU
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post #30 of 40 (permalink) Old 04-18-2020, 04:11 PM Thread Starter
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One time I had a leak and I couldn't figure it out. I ended up replacing the plastic O-ring on the cylinder with this and the leak stopped.

https://www.amazon.com/Leak-Stopper-.../dp/B018UNZLHU

Just ordered, I've heard others mention this. Thanks.
(Haven't gotten to the tank yet to check for leaks, will later today)
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