Mist Method

[Purrbox]

I decided to give the mist method a try, but the implementation isn't turning out as easy as it sounds.

I've got a Sweatwater Diffuser and ViaAqua 180 Waterpump with the diffuser is directly below the waterpump. The problem is that the waterpump doesn't seem to want to suck in the CO2 bubbles so that it can blast them around the tank. They hit the bottom and roll of to one side or the other.

I've thought of a few possible problems and would appreciate some input from those of you who've got this method working.
1. Not enough distance between the waterpump and the diffuser? (Currently about 0.5-1")
2. Waterpump is either not powerful enough or not designed well to draw in the CO2 bubbles?

Thoughts and input?

If I can't get this resolved soon I'm going to have to switch back to using my inline reactors, as my current CO2 levels are extremely poor.

 

[David14259]

What about some sort of cone shape on the bottom of the waterpump to catch the bubbles and channel them into the intake of the pump?

 

[GlitcH]

I'm not familiar with that pump.

What size tank is this in?
Would a powerhead be out of the question?

 

[Purrbox]

Here's the info on the ViaAqua waterpumps at DrsFosterSmith. While they're called waterpumps they can also perform as powerheads and come with lots of extra pieces to allow for different configurations. The 180 model provides 80GPH and creates plenty of flow in my aquariums.

We're talking about my 2.5, 5.5, and 10 gallon aquariums. I really don't think that more flow is an option.

 

[Plantbrain]

You might try using a Rhinox diffuser instead, say a 1000 series.

They seem to work very well and are nice looking, last a long time etc and are cheap!

Tom Barr

 

[Peyton]

Purrbox, you could cut a little piece out of the plastic strainer there on the intake of the pump just large enough to pass the CO2 tube into. Then you can just skip using the diffuser all together.

 

[Purrbox]

What is the benefit of the Rhinox Diffuser over the Sweatwater Diffuser? How would it help to overcome the issue that the bubbles aren't getting sucked into the waterpump?

Peyton - While your suggestion is valid, it really wouldn't be the mist method of diffussion as I understand it. Rather that would be using a powerhead/waterpump as a powered diffuser.

 

[An t-iasg]

Here's a picture of my setup that I posted in another thread:
http://www.aquariumadvice.com/viewtopic.php?p=799806&highlight=#799806

My pump is a little Marineland Mini Jet. When I invert the pump intake over my diffuser, the intake is in just the right place to capture the CO2. If you like this idea, you'd have to buy a new pump but it's not expensive. I have mine at about medium flow in my 10 gallon.

I have some Via Aqua pumps too and I love them for pumping new water into my tank, but their intake is more spread out than the Mini Jet's intake.

 

[Hoovercat]

The pump you have looks like a Rio. The last rio I bought had a venturi fitting that attached on the output side. It lets you connect an air line to feed bubbles into the pumps output. I would use that to feed CO2 and drop the sweetwater stone.

 

[Purrbox]

These pumps do come with a venturi fitting. Unfortunately they don't come with any instructions and I haven't figured out how I'm supposed to be able to connect the venturi to the pump.

 

[Hoovercat]

Care to post a pic with the parts they sent in it?

 

[Purrbox]

Actually I think I found a way to get the venturi connected. It's not real secure, but it does seem to be working. I'll see what the CO2 levels are like by tomorrow night.

 

[Peyton]

Peyton - While your suggestion is valid, it really wouldn't be the mist method of diffussion as I understand it. Rather that would be using a powerhead/waterpump as a powered diffuser.

I guess I don't fully understand it then. Why run it through a diffuser only then to spray it around the tank through a powerhead? Is it to achieve smaller bubbles going into the pump or to distribute dissolved CO2 along with the undissolved bubbles throughout the tank?

 

[Hoovercat]

distribute dissolved CO2 along with the undissolved bubbles throughout the tank?

you answered yourself, sort of.

 

[Peyton]

distribute dissolved CO2 along with the undissolved bubbles throughout the tank?

you answered yourself, sort of.

OK, I understand. I've just been using a powerhead and have been getting great results that way. I've had some of the most compact large growth this way than with any other I've tried.

 

[Purrbox]

The purpose is to blast a fine mist of CO2 bubbles throughout the tank. Theory behind it is that the plants may be able to better use the gaseous CO2 than dissolved CO2 if it comes in direct contact with their leaves. The actual reason that it works is still unproven, but it has been proven one of the most effective methods injecting CO2 into an aquarium thus far if set up correctly.

With the size of my aquariums it doesn't look like I'll actually end up achieving the true mist method, as my bubble rate is simply too low. But perhaps it will still work. Either way it was worth a try and I'll know whether or not to bother with this method in smaller tanks in the future.

 

[Plantbrain]

I think both dissolved and gas phases are present in every case.
It's difficult to isolate one without dissolving some gas into solution.
So setting up a control for gas phase only is nearly impossible.

What can be done is compare the O2 levels between the dissolved CO2 and then maintain that same dissolved CO2 level, and add mist.

If there is an increase in O2 levels, then we can say the method itself works.
I've found a 20-40% increase in O2, thus that is easily transferred to 20-40% increase in plant growth.

The theory part I'd first started with was that gas can transfer across a boundary layer much faster than than a liquid, and that is true in theory. I'd also suggested that the CO2 mist had a higher concentration than the water, this too is likely.

One thing that may be occurring is that the mist bubbles break up the boundary layer surrounding the leaves and helps to exchange the dissolve CO2.

This may be addressed by using air or an inert gas such as Helium which is relatively simple and cheap to add and non toxic. That would break up the boundary layer, but would not increase growth due to added CO2.

If there is no net gain in O2 production, then we can likely rule out the boundary layer issue as a reason. Physical chemistry kinetics clearly shows a much fast transfer rate, about 10,00 faster for a gas phase versus a liquid phase in diffusion.

The same is true as to why the atmosphere does not provide plenty of CO2 for submersed plants, but seldom is limiting for terrestrial plants. The rate of exchange, or flux, is too slow to keep up with demand.

While I can isolate the boundary layer issue, and show that there is some effect in increased plant growth, and I can show that is will produce localized effects in a larger tank, I cannot show what fraction of gas vs the dissolved form the plant gets.

I am unaware of any method that may answer that question.
Isotopic labeling will not do it. What labels are there would show that the CO2 was gas or liquid when the plant assimilates it?

Nothing I know of.
We can collect the mist itself at various times and flow rates and measure it's content.

That+ ruling out the boundary layer effect+the O2 readings between treatments, + localized effects can lend more support to the theory.

Another approach to see about the gas phase that isolates just that, although only for a little fraction of time, is exposing the plants to air when doing a water change and misting them with water to keep them from drying out.

Wait, then refill the tank and measure the O2 levels/pearling at midday.
You can also do this same water change method(typically 80-90% to exposure the plants well) right before the lights come on. If you see no bubbles forming after 10-60 minutes, then you know it's not degassed tap water, the increase in pearling you see in the middle day is due to the exposure to air and the CO2 uptake.

You should also see a gradient of pearling as well, you can do a 50% water change and exposure some plants, and not others and see the exposed plant pearl a lot more than those that were not.

Some suggest that the since the plants are closer to the light, they will pearl more than those lower, a simple solution is to use something that pearls a great deal but lacks roots like Riccia, and take it out of the tank for a period of time and keep it moist, then return to the tank vs the same Riccia that was not taken out and is at the same depth/light intensity.

Regards,
Tom Barr

 

[Zezmo]

A brief comment on mist method, I have it running on two of my high tech tanks. On one, I no longer use a diffusor and simply bubble CO2 directly into the intake of the powerhead. The impeller does a great job of chopping up the CO2 and blasting it all over.

In the other tank, I use a water pump, it is a cube type nano. In that case I drilled a hole in the side of the pump near the impeller, and let the co2 bubble in directly to the impeller. Again, a fine mist is propelled throughout the tank.

 

[Purrbox]

Well it looks like semi jury rigging the output of the waterpump to attach the ventri worked to get my CO2 levels back up where they need to be. (I REALLY like my new CO2 Drop Checkers!) It's not really a true mist method since the CO2 is getting disolved before it reaches the spraybar, but it seems to be effective. I think that if I play with the positioning of the spraybar a little bit, I can probably improve the CO2 levels a touch more.

 

[zenkatydid]

i, too, use the co2 tube directly into the back of the powerhead (i cut away a hole and stuck the tube straight in there). my tank is constantly littered with millions of tiny bubbles - i can't imagine a better way of diffusing it. i have 4 2l bottles of co2 and get 30-45ppm.