Conversion of powerhead venturi to waterfall

[Dane]

Hey guys,

I keep my 17gal tank in my room, and it gives me a lot of satisfaction
Its running an internal powerhead filter, which I find to be very silent, *except* for the bubbles from the venturI system (sucks air in through a pipe, then blows bubbles through the main outlet back into the water)

I want to know if I close the venturI inlet, and run a pipe from the outlet above the water surface with a wide rI'm to create a waterfall instead, will that be enough to aerate the water? Keeping in mind the only thing that actually aerates your water is surface agitation (ie: the bubbles from air stones don't aerate the water until the breach the surface)
OR could I simply raise the head of the outflow so that its level with the water surface, this should cause considerable disturbance...

Has anyone else tried this? Would appreciate your input,
thanks, Dane

 

[Steve113]

1 - Bubbles do aerate the water, and they do so in 2 ways. The bubble as it is rising will diffuse some oxygen into the water as the air is still in contact with the water. This is admittedly for a short time due to the speed at which they rise, but the smaller the bubbles the slower they'll rise and thus increasing the time that the air is in contact with the water around it.

The bubble when it breaks the surface creates surface agitation which increases the surface area of the water and thus helping to improve the aeration process.

Aereation is all about surface area and contact between air and water to allow diffusion of gasses into the water - pumps and air stones are just a mechanical way to increase this surface area to aid in this process.

2 - With regards to your waterfall Idea, you could set sumething like this un your tank, but why not just gat an overhead trickle filter which does this for you, they are quite cheap. or use your internal filter if it's design will allow (place the output nozzle above the water line)

- You said the tank was in your bed room; What I will say is that it may seem like a good idea now, but believe me, you will be driven insane by the water noises as you try and sleep.
I speak from experience here - I have a trickle filter in the tank in my room and I now overfill my tank so as to minimise this effect!

 

[Blub]

My fish are fine with just the powerhead running underwater. I have never had to go to any lengths to aerate my water, I'm glad to say so I don't see why you should if your tank is sensibly stocked.

 

[Lucy]

HI Dane, I merged your threads. It's best to have one thread for the same topic.

 

[Dane]

thanks kindly lucy, I tried to see if I could move my thread myself, after I saw that there was a forum for this specifically. Could not, so I reposted ;-)

@steve - I was under the impression that while gaseous exchange occurs at the surface of any body of water, it is surface agitation that is key - particularly breaking surface tension, and while i'm sure the bubbles themselves do contribute to gaseous exchange, it would be very minor indeed.
And I know what you mean about the noise at night, but I've had my tank for nearly three months and it doesn't bother me at all, but maybe that's just my late night thesis-crunching sleeping habits...

@Blub, I actually spoke to the guy who runs a specialist fish shop at length, and he also said that the powerhead running alone should be enough, that the venturI would be unecessary. Do you angle your powerhead outlet so that it ripples the surface or is it totally submerged? Is the tank quite understocked?

 

[Steve113]

the surface agitation would contribute a great deal, but the submerged bubbles also help (although only slightly) - you can get special diffusers that work by making the bubbles smaller and keeping them under water for as long as possible for this purpose.

This is an example of such a device - this can be used for diffusing gasses into the water for example. Works well, and they also look very cool in action!




I think we're both kinda right in this respect.

And yeah you should point your outlet to the surface to maximise the gas exchange as you've stated above

 

[Dane]

Agreed, although the device you showed is not a diffuser at all, its a C02 bubble counter. The diffuser will usually have a mechanism to break the bubbles as small as possible, much smaller than a normal airstone - for the exact reasons you stated. But these diffusers are specifically for C02, never heard of them being using to oxygenate your tank. This is because carbon dioxide is much more soluble in water than oxygen (more than twice as soluble actually).

Thanks for the advice all

 

[Steve113]

Yeah that device is for co2 - hence:

...you can get special diffusers that work by making the bubbles smaller and keeping them under water for as long as possible for this purpose.
This is an example of such a device - this can be used for diffusing gasses into the water.

I was merely trying explain the concept with a visual aid. I am aware that it is not for O2.

I see that I have actually linked to the wrong also! There was one similar which broke up the air into tiny bubbles but also had the coil. I'll see if I can find it for you...

I wonder how successful it would be for aeration though? I'd like to give it a try as they do look pretty smart.

 

[Steve113]

Ah, here we go...




although this one is described as for use with CO2 also, it illustrates my point and I have seen similar devices for aeration.

 

[Dane]

yeah! that's the one I was talking about. Hehehe, I think we're getting a bit carried away here tho - I merely said at the beginning of the thread that the main cause of aeration is surface agitation, not from the actual bubbles being in contact with the water. I still reckon even if you were to use one of these diffusers for oxygenation you'd have poor results, due to O2's poor water solubility. You do get diffusers for aeration;

or

but again, I think these are more for the look, and will contribute more to aeration through surface agitation.

Wow, we are so off topic now. Maybe should start a new thread on converting a CO2 diffuser for aeration...

 

[Steve113]

Hmm...
I guess you're right.

As for the original waterfall idea, Had you thought of the added noise as a problem?

 

[Dane]

Well, I wanted to do a waterfall that runs down a tray, so it doesn't "fall" straight into the water, hopefully that will be quieter than the bubbles from the venturi. Right now I've turned off the venturi, and have just angled the outlet so that it breaks the surface of the water. I wish I had an ox test kit, but the fish seem perfectly normal... If its fine like this then I won't need to bother with the waterfall... hehehe

I dig the look of your aquariums by the way, black substrate looks fantastic!

 

[Steve113]

Thanks,
glad you lke it.

I was actually thinking about changing it to a natural sand colour (the black really does show up the debris on the tank floor)

As for my pics, the one labelled "latest 200l" is how it is set up now - the others are just as I was starting out

 

[Dane]

Yeah, natural substrate is my favourite, my tank is black backed with earthy/rusty/orange coloured gravel. Good luck if you make the change

 

[Blub]

@Blub, I actually spoke to the guy who runs a specialist fish shop at length, and he also said that the powerhead running alone should be enough, that the venturI would be unecessary. Do you angle your powerhead outlet so that it ripples the surface or is it totally submerged? Is the tank quite understocked?

In 1 of my tanks (Largest - 47gal) I have the powerhead angled up. It is heavily planted, and the plants take in oxygene in the night, but put oxygene in in the day, so it's fine even with the decreased oxygene at night! It also has about 10" over the 1" per gal guideline.

In my other 2 tanks, the powerhead is horizontal, but creates surface agitation.

In a bedroom, I wouldn't bother with aeration, as the noise it makes is boud to keep you awake at night. (I have an aerator, but since all the tanks are in my room I don't use it)