Low Tech Co2 Idea?

[Mcbenthy]

I am currently in the middle of the planning stage for my low-tec 50gal tank. Stocking has been pretty much decided upon, and the plant list is almost done.

What I am wondering is whether adding a bubble wall would help the plants? Being low tech I am not adding CO2 via a diffuser or a liquid addative (although I may dose flourish to begin). The substrate is going to be soil and I am planning to follow the Walstad method.

The idea with the bubble wand would be that the high surface area caused by the bubble will allow a much quicker re-equilibriazation of water:air gases. The hope being that it will keep the CO2 levels up in a low tech system in much the same way that it would keep them down in a high-tech system.

The reasoning behind it is that Walstad clearly shows the drop off in CO2 throughout the day as being a limiting factor in plant growth, and I got thinking about where you see large amounts of aquatic/emersed plants. In still water obviously you get reed beds and floating plants, but in faster flowing water you seem to get much stronger and vibrant growth just downstream from waterfalls, something I would attribute to the falls allowing a much better enviroment for the dissolution of CO2 into water.

Am I completely wrong? any experiences?

Cheers

 

[sjdriscoll]

I put my CO2 into my filter inlet pipe - that way it spends a lot longer in the actual water and the larger bubbles that make it through the filter get 'smashed' up by the impeller. I get a fine mist at my outflow and the CO2 has already been in the water for a minute or so. The finer bubbles also get trapped in the surface film and (I'm guessing here) will have even more opportunity to be dissolved into the water column.

It's like a waterfall - but in my filter!

Steve

 

[TheRedDarren]

That doesn't affect your filter adversely then? Just wondering as the bacteria are aerobic?

 

[Doc7]

that shouldn't affect them


For tanks without CO2 injection via DIY or Pressurized, you are correct that increased aeration is the way to go.

Probably easier/better to use your filter outlet for this effect instead of a bubble wall. Lots of surface agitation will be how you get the CO2 in equilibrium.

I personally run a high-surface-agitation tank even with CO2 injection. CO2 is so cheap that I can just bump up the flow rate and maintain the same concentration of CO2 in the tank, while also having beneficial oxygen levels as well.

 

[Mcbenthy]

I put my CO2 into my filter inlet pipe - that way it spends a lot longer in the actual water and the larger bubbles that make it through the filter get 'smashed' up by the impeller. I get a fine mist at my outflow and the CO2 has already been in the water for a minute or so. The finer bubbles also get trapped in the surface film and (I'm guessing here) will have even more opportunity to be dissolved into the water column.

It's like a waterfall - but in my filter!

Steve

Nicely! I know that it's all aout surface area, so fine bubbles of pure CO2 will lead to a massive increase in the rate of uptake

That doesn't affect your filter adversely then? Just wondering as the bacteria are aerobic?

I would be surprised if it effected them, the levels are still very low, and the dissolution of CO2 doesn't kick out the dissolved O2

that shouldn't affect them


For tanks without CO2 injection via DIY or Pressurized, you are correct that increased aeration is the way to go.

Probably easier/better to use your filter outlet for this effect instead of a bubble wall. Lots of surface agitation will be how you get the CO2 in equilibrium.

I personally run a high-surface-agitation tank even with CO2 injection. CO2 is so cheap that I can just bump up the flow rate and maintain the same concentration of CO2 in the tank, while also having beneficial oxygen levels as well.

Nice to hear! I'm still not sure how to do this, air stone or surface agitation. Will proably be a case of what I feel looks better. I was thinking a long bubble tube that could just be set against the back wall behind some big plants...

 

[Primous]

Has anyone tried using the the spray bar of their external filter with the spray bar angled down slightly. I started this method in my aquarium and had such a high diffusion rate that I saw pearling in my aquarium for the first time. A vid example...

From the 2:43 - 3:53 mark

 

[Mcbenthy]

Has anyone tried using the the spray bar of their external filter with the spray bar angled down slightly. I started this method in my aquarium and had such a high diffusion rate that I saw pearling in my aquarium for the first time. A vid example...

I can't see the vid, so apologies if it is explain in that, but are you injecting CO2 inline? If so then the angled spraybar would allow a higher concentration of CO2 to buildup (lower partial pressure close to the surface = less diffusion out). Also it could be a result of a better flow distributing nutrients around the tank more effectively?

 

[Doc7]

I put my CO2 into my filter inlet pipe - that way it spends a lot longer in the actual water and the larger bubbles that make it through the filter get 'smashed' up by the impeller. I get a fine mist at my outflow and the CO2 has already been in the water for a minute or so. The finer bubbles also get trapped in the surface film and (I'm guessing here) will have even more opportunity to be dissolved into the water column.

It's like a waterfall - but in my filter!

Steve

Nicely! I know that it's all aout surface area, so fine bubbles of pure CO2 will lead to a massive increase in the rate of uptake

That doesn't affect your filter adversely then? Just wondering as the bacteria are aerobic?

I would be surprised if it effected them, the levels are still very low, and the dissolution of CO2 doesn't kick out the dissolved O2

that shouldn't affect them


For tanks without CO2 injection via DIY or Pressurized, you are correct that increased aeration is the way to go.

Probably easier/better to use your filter outlet for this effect instead of a bubble wall. Lots of surface agitation will be how you get the CO2 in equilibrium.

I personally run a high-surface-agitation tank even with CO2 injection. CO2 is so cheap that I can just bump up the flow rate and maintain the same concentration of CO2 in the tank, while also having beneficial oxygen levels as well.

Nice to hear! I'm still not sure how to do this, air stone or surface agitation. Will proably be a case of what I feel looks better. I was thinking a long bubble tube that could just be set against the back wall behind some big plants...

Surface agitation is pretty :

I inject CO2 via a "Rex Reactor" into the outlet of my eheim, which causes this surface agitation. Lots of oxygen bubbles coming off the plants, no visible CO2 bubbles coming out of filter.

It takes me more CO2 to get to 30 PPM in water due to my agitation but there's no downside to extra O2 and the CO2 only costs a few bucks a month anyway.

 

[Doc7]

If you're not injecting pressurized CO2, there is no air stone out there that will give you the same surface agitation a filter outlet will. In my case I use the spray bar for agitation (but less than I would if I didn't have pressurized CO2, which i do). A HOB filter could also work with slightly lower water levels. But with a spray bar you can have massive amounts of agitation which is what you want if you have no way to inject CO2 other than equilibrating with the air. Additionally you'll oxygenate your water which is good for fish and plants.

Without pressurized CO2 injection, there is 0 downside to any amount of excess agitation. That's the only way CO2 gets into your water.

 

[Mcbenthy]

If you're not injecting pressurized CO2, there is no air stone out there that will give you the same surface agitation a filter outlet will. In my case I use the spray bar for agitation (but less than I would if I didn't have pressurized CO2, which i do). A HOB filter could also work with slightly lower water levels. But with a spray bar you can have massive amounts of agitation which is what you want if you have no way to inject CO2 other than equilibrating with the air. Additionally you'll oxygenate your water which is good for fish and plants.

Without pressurized CO2 injection, there is 0 downside to any amount of excess agitation. That's the only way CO2 gets into your water.

The airstone wouldn't be there to cause surface agitation, it would be causing an increase in surface area through the bubbles. so instead of just the water surface to have gasseous exchange over (3ftx1.5ft ~ 1mx0.5m = 0.5 m^2), I would have the surface + the surface area of the bubbles as they travel up through the water column (3ftx1.5ft + 0.141 m^2 from bubbles (assuming 1mm radius, 15 cm wand, 60cm height, ~40% occupancy of bubbles in the water column, 2D plane only considered - significantly higher number if depth included, this assumes a layer of 2mm thicknes, 1 cm thickness wand would have 5x greater surface area) = 0.641 m^2)

 

[Doc7]

You're thinking too much...

The gas doesn't really dissolve that well as the bubbles rise through the water. The reason people use bubble wands when it comes to planted tanks is to cause, or increase, surface agitation with them.

Filter-driven surface agitation is a much better way of causing this agitation, and thus a better way of doing what you intend to do.

Plus - a bubble wand in an El Natural tank can look a bit silly in most displays, and the air pump is seldom as silent as a filter.

It's your tank though : )




EDIT :
Regarding your math.... Surface agitation increases, umpty-fold, the amount of surface area of water exposed to the air. Sure, 3 x 1.5 feet is exposed at a given instant but with agitation you are pumping hundreds of gallons per hour from the CO2/O2 depleted bottom areas of the tank to the surface where they will contact the air and absorb gases.

Bubbles rise straight up in an extremely narrow band of your water column, and too quickly to allow much absorption. This is why CO2 bubbles in pressurized setups are directed to filter inputs or outlets, to put them into the water column. You'll find that your bubble wand bubbles rise right through the increased current and don't absorb into the water like pure CO2 bubbles do.

 

[Mcbenthy]

You're thinking too much...

The gas doesn't really dissolve that well as the bubbles rise through the water. The reason people use bubble wands when it comes to planted tanks is to cause, or increase, surface agitation with them.

Filter-driven surface agitation is a much better way of causing this agitation, and thus a better way of doing what you intend to do.

Plus - a bubble wand in an El Natural tank can look a bit silly in most displays, and the air pump is seldom as silent as a filter.

It's your tank though : )




EDIT :
Regarding your math.... Surface agitation increases, umpty-fold, the amount of surface area of water exposed to the air. Sure, 3 x 1.5 feet is exposed at a given instant but with agitation you are pumping hundreds of gallons per hour from the CO2/O2 depleted bottom areas of the tank to the surface where they will contact the air and absorb gases.

Bubbles rise straight up in an extremely narrow band of your water column, and too quickly to allow much absorption. This is why CO2 bubbles in pressurized setups are directed to filter inputs or outlets, to put them into the water column. You'll find that your bubble wand bubbles rise right through the increased current and don't absorb into the water like pure CO2 bubbles do.

Good shout on the math, whilst the surface area increase from the bubbles is high, the local water will quickly be saturated, and then I either have to blow the bubble round my tank (naff) or have a slower diffusion. Maybe I'm underestimating surface agitation, it just doesn't feel like it will be enough to compare to bubbling air... gahhhh!!!

from an increased agitation view, what kind of levels of turnover would you feel is good/ I'm currently planning on having ~10x filter turnover, but also have an additional powerhead of needs be...

 

[Doc7]

Strong rippling across the surface is all you need.

I run an Eheim 2217 and an Eheim 2215 on my tank which i think gives me something around 420 GPH. But again - asking how much turnover when it comes to surface agitation is subjective, because I could point my spray bars down at a 10 degree angle and have a mirror-smooth surface, or up around 30 degrees like I do and have a strong ripple throughout the tank.


Get appropriately sized HOBs and/or canister filters for your tank size (read around) and you'll be able to get the agitation you want.



Bubbling air through the water won't do much for you at all, so don't try to compare it to agitation : )

Even pure CO2 wouldn't work if it was just bubbled up through the water, that's why people inject it directly into their filter lines or bubble it through the tank into the inlet or outlet flow of a filter. It wouldn't work if they just bubbled it right to the surface, similar to how an airstone works.