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Discussion Starter #1
I haven't been able to find any articles on this; so I thought I'd see what people here thought. I recently decided to start a high tech pressurized 40G tank. And was trying to decide what sort of diffuser to by, when it occurred to me that I might not need to by any at all. In stead I decided to use the underside of rocks in my tank as a simple bell diffuser. So far it seems to be working. At 1bps I'm sitting at 14.85 ppm of CO2. At 1.25 bps I get a little over 18ppm. Can anyone think of why this is a bad idea, or why it isn't done more often? Or is it done all of the time and it's just so obvious that no one mentions it? In the photos I've attached, you can see the CO2 bubbles by the gourami in the back. The large stone I use is very slightly cupped on the underside, and set on the other rocks in a way that maximizes the amount of time a bubble spend underneath it. which for all intents and purposes is pretty much all day. When the CO2 kicks off at night most of the remaining bubbles are gone by morning.

Tank is still a work in progress, but comments obviously welcome...
 

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Because the surface area of the trapped bell of CO2 is miniscule compared to the surface area of the same amount of CO2 broken up into thousands of bubbles. And without constant water flowing past the bell of CO2, you'll get a localized saturation of aqueous CO2 right next to the bell which slows down more dissolution of CO2. But if you increased water flow underneath the rocks, the trapped CO2 would simply be blown away.
 

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Discussion Starter #3
As an FYI my HOB dumps right behind this rock, so there is a constant current underneath it, so I'm not getting any point source differences in ph readings from differing places in the tank. I understand the differences between bell and bubble diffusers, that doesn't mean bells don't work. And I'm pretty happy with [email protected] What's a typical ppm for 1bps in a 40G? I see a lot of people running 2 bps and talking about 30ppm. So I've figured I'm fairly on track, and not comparatively wasting that much co2 esp. when compared to a bell.
 

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Discussion Starter #5
How are you measuring your CO2 levels?
calibrated Ph meter, and liquid API tests. API KH test. Adjusted for TDS and temp. I've been spot checking water samples from various locations during the day every hour for a a few days. Mostly to make sure I wasn't killing the fish since I'm new to the co2 thing.






Co2=15.664*KH*POWER(10,((-14.8435+3404.71/(((TEMP_F-32)5/9)+273.15)+0.032786(((TEMP_F-32)5/9)+273.15))+(-0.0230848+-14.3456/(((TEMP_F-32)*5/9)+273.15))*POWER((TDS/1000),0.5)+(0.000691881+0.429955/(((TEMP_F-32)*5/9)+273.15))(TDS/1000))-PH)
 

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Discussion Starter #6
So, I've spent the last week trying to verify my Co2 levels. Esp rechecking my pH readings. As well as doubling the bps to 2. Looks like my pH reading were off just a hair, but enough to throw my cO2 calculations pretty well off. Based on this last week, by using the bottom of the rocks I'm only able to 11-12 ppm of co2 in my 40G. Not long after 2bps my bubbles don't really stay under the rocks very well. So it really does seem like a waste.

My original question was really more from a fish/tank safety point of view as whether or not this was a bad idea. So Although I have about a square foot of under rock surface to work with there's really not enough control to make it worth while. Nor are the aesthetics worth it as I'd really have to have a bubble-wall of co2.

Switching to a canister and an atomizer to see if I can get some better growth. Thanks for the input.
 
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