Thoughts on an airstone and lack of biowheel

[isu_guy]

Ok, from everything that I've gathered a biowheel is far superior to a "normal" hanging from the back of the aquarium filter. This is supposedly true for multiple reasons, one being that there is more oxygen present (which is needed) for the bacteria to breakdown both ammo and nitrite.

And I've heard with no real proof, but it could be believed, that the airstone can be a bit annoying to fish, they might like a break from the noise from time to time.

So I was thinking-
If the purpose of the airstone is to introduce more oxygen, and bacteria benefit from having more oxygen than they would normally get from just the tank water, and perhaps the fish would rather not live with the noise from the air bubbles, why not just put the airstone in the hanging filter?

I figured at very least it couldnt hurt, so I did it the other day. There has been a debate whether or not it is from the bubbles of the disturbance of the surface that promotes gas exchange (and in most cases, read," introduction of oxygen"). So either way there still is a surface disturbance, even if it is in the hanging filter- which should equate to more oxygen.

After 4-5 days I've checked my levels and my water seems fine (not to any surprise). I don't know if this helps any but I figure if the biowheels claims of so much better oxygen supply are true that perhaps I'm on to something.

Any thoughts

 

[enchanted]

Alright, first you don't need an airstone if you have a good filter, which it sounds like you do.

The way a bio-wheel works is to be "THE" source for all the bacteria necessary for a tank and to keep that bacteria in constant contact with the tank water and the air.

That is why they work so well. You could take cycled bio-wheels off a tank and put them on a brand new setup and probably never see a spike. I know because I did it and nothing spiked whatsoever when I brought up my 125 Gallon. And that was a pengiun 330 rated for only 75G I think at most.

As for the sound, I don't know.

As for oxygen in the water your filter takes care of this by causing surface agitatoin. Bio-Wheels do it more because not only do they agitate the water at the tank surface but also as it is going past the bio-wheel.

 

[teacherspet]

If you took the bio wheel off to put on another tank, would it affect the tank your removed it from? I was thinking about doing this for a new tank but thought it might hurt the old biological filter.

 

[enchanted]

As long as you have older (2 weeks or better) filter media in the old tank you should be okay.

Personally I run a 330 and if I setup another tank w/ a Penguin and not a canister I will just pull one of them like I did for my 170 on my 30 Gallon.

 

[isu_guy]

ok, first of all, I have a hard time buying that surface disturbance (agitation) is the only reason for gas exchange. The smaller the bubble the more surface area created by the airstone. Obviously it would depend on a lot of things but there is a very good chance that on a given tank there exists more surface area between gas and water on the bubbles than on the entire water level of the aquarium. To think that no gas exchange is happening as the many small bubbles rise to the surface and only at the time when they break the surface of the water level does any gas exchange happen; to me that seems a bit ridiculous.

perhaps I'm getting off topic though.

 

[ddm18]

isu_guy, just to continue off-topic, briefly. I've thought the same as you, about bubbles surely giving a good gas/water surface area, but (and this is entirely a guess), maybe the point is that it takes time for oxygen to dissolve into the water, meaning that for the 1-2 seconds that the bubbes take to rise through the water isn't long enough for any considerable amount of oxygen to dissolve. As I say, it really is a guess, and I have no idea.

Having said that - I have 2 airstones running in my tank, which I'd really rather weren't there, but I'm terrified that I'll take them out and wake up the following morning with a tank full of dead fish!

Does anyone know if there's any kind of oxygen test kit (or any other way of testing for oxygen levels) available?

 

[isu_guy]

ddm18,
yes any given bubble only has a second or two to exchange gas, but I believe that gas exchange would happen at a constant rate given a surface area that has not developed a stagnant surface tension. This being said, any given bubble does not have much time to exchange gas, but over all the total surface area of all the bubbles stays fairly constant (for every bubble that reaches the surface there is another bubble coming out of the airstone - give or take).
What I'm getting at is the exchange of gas does not take a second or to to "get going" before any gas is exchanged, kinda like acceleration due to gravity, as soon as you let go of something it begins to accellerate unlike how the cartoons depict it where wiley cyote has time to pull out a "yikes" sign before he plummits.

We could do an experiement to find out if the exchange of gas happens during the bubble stage of things. Heres how it would go:

Instead of the normal air that is pumped through the airstone we could pump pure C02, then at the top of the tank we have a strong fan to dispperse away the CO2. The air at the surface of the tank would be very close to rooms ratio of O2 to CO2 (slightly higher due to the CO2 coming from the pump, but this should be negligable because the fan would be set at a very high level). We would have a normal tank setup with a pump pumping room air. We would check the levels of O2 and CO2 before the start and after many time intervals. IF gas exchange was due to surface agitation alone, then the levels should be very similar to the control tank, if gas exchange happens from the bubbles (which is my hypothesis) then the control tank would have a higher level of O2 than the experimental tank and the exp. tank would have a MUCH higher level of CO2.

Anyone who thinks that gas exchange only happens due to surface agitation want to volunteer?


ddm18- you said that you wished you could take out the airstones? If they fit in your filter you could put them in there, whether I'm right or wrong about it, there still is surface agitation (which I believe promotes gas exchange, but is not the sole factor in gas exchange), and that agitation introduces more O2 into the water which gets immediately pumped back into the rest of your tank.

 

[freddyk]

I know most bio-wheel users won't agree, but experimenting with both I'm convinced there is no difference between them. The bio-wheel was an excellent way for marineland to compete with their competitors, as the logic makes sense.
-if there is not enough oxygen in the water to support a bacteria colony without exposing it to air, then there isn't enough for the fish
-the simple act of pouring the water back into the tank provides plenty of aeration in the tank, with or without the bio-wheel

I use nothing but aquaclear filter and canister filters, no bio-wheels, no airstones. The filters add plenty of oxygen, bio-wheels fixed something that was never broken to begin with. I'm certainly not saying there is anything wrong with them either, of course.

Teacherspet, I'd be very hesitant to remove a bio-wheel from a filter meant to function with it.

 

[Tolak]

Or you could toss in an airstone, put a sheet of saran wrap on the top of the tank with a hole the size of the airline leading into it to allow only the air from the airstone to have contact with the water. Seal up that surface & see how long before your fish are floating at the top looking for more O2. Bet it won't be long. Any takers on this one?

Tolak

 

[sylvia]

I don't know about that last bit I wouldn't dare try it... However, some of the gas that pops at the surface may contain enough oxygen to, coupled with surface aggitation from the bubbles themselves, sustain a few fish but unlikely a fully stocked tank.

Some oxygen DOES get into the water from the air bubbles as they rise. However, it is when the bubbles pop at the surface, causing a significant increase of surface area, that most gas exchange occurs. So air bubbles DO help - by incresing surface area significantly.

Having said that, I only ever use airstones in tanks without filters (breeding tanks) and my filters provide enough surface aggitation to sustain both fish and bacteria. I'm positive adding an airstone would make absolutely no difference to my fish or water quality.

 

[enchanted]

I never said their wasn't enough air in the water to sustain the bacteria.

What I said was a filter provides enough surface agitation and a bio-wheel provides a bit more agitation to the water to increase the exchange of gases.

That being said, as to the bio-wheels. Take out all your filter media, clean your filter and put it back together on a non-bio-wheel filter and watch your tank mini-cycle. I've done it.

Now, do the same thing with a Bio-Wheel filter, but don't clean or change the bio-wheels, no mini-cycle.

Basically you have just done the same thing to both filters with full replacement of the media and a full cleaning of the filter, but the filter without the bio-wheel will mini-cycle because there is no bacteria left.

Now, also a bio-wheel filter "DOES" provide better bacterial work. If you don't believe you can do the research as I have done to understand the bacteria, how it works, and why this is a fact because I already know and to be honest I'm not going to sit here and argue over something like that.

You do not need an airstone in a tank with a good power filter (hob or canister) if they are causing surface agitatoin.

I have first hand experience in this and I had the same question a while back and tested and found out I didn't need it.

If you are running a breeding tank, etc.. then you probably would want an airstone along with a sponge filter, but that is a different area.

 

[Bignose]

This is a very interesting question about how much gas really escapes the bubble. If the water is completely pure of all dissolved gases, or equivalently, saturated with pure nitrogen and no oxygen, the transfer of oxygen out of the bubble can be estimated by:

N = c*sqrt( (4*D*V)/(pi*db) ) * pi * (db/2)^2

where

N = rate of which gas leaves the bubble and enters the water per unit time
c = concentration of gas in the bubble initially (in the atmosphere)
D = diffusion constant for gas in the water
V = terminal velocity of bubble (which is achieves quick, so, really its speed)
pi = pi, you know, 3.14159 and all that
db = diameter of the bubble

Now, the bubble takes H/V time to get to the top of the tank, (H = height of tank)

So N_total = c*pi*(db/2)^2*H*sqrt(4*D/V*pi*db)

This result was published by Hammerton and Garner in 1954, and their experiments found it valid for bubbles of 3 to 5 mm.

Just throwing some estimates together, I get on the order of 10^-10 g or 0.00000000001 g of oxygen from each bubble. And, that is only if the water is completely devoid of oxygen... since the water most of the time will have some dissolved oxygen in it (hopefully for our fishes about as much as it possibly can!)the transfer of one bubble is very small. In fact, as more oxygen gets into the water, the amount transfered out of the bubble decreases exponentially.

Now, there are many bubbles... but the estimates above say it would take over a million bubbles to get one milligram of oxygen into the water. And, at 25 degrees C, the oxygen saturation is about 8.2 ppm or mg/L.

So, you would need more than 8.2*(Liters in your tank)*(1 million) bubbles to completely saturate your tank. It would take quite some time for that many bubbles -- indicating that the surface gas exchange is very significant.

 

[isu_guy]

Why thank you for all the research. to take it a step farther,

The following will be based on your findings and on using a Rena Air 100 (for use with 10-25 gallon tanks) and a 20 gallon tank (I just did a search on the first pump that came up and chose 20 for no real reason, but its at the high end of the pump use, so there is a fair amount of conservatism)

the pump flows at 120L/hr. Using 3mm diameter bubbles each bubble has a volume of .014137 ml. (Volume = 4/3*pi*r^3, r=1/2 diameter, 1cm^3=1ml)

Therefore the pump will generate 8,488,264 bubbles/hr. (120L/hr * 1000mL/L 1bubble/.014137mL)

a 20 gallon tank is equal to almost 76 Liters, so using your
"8.2*(Liters in your tank)*(1 million) bubbles to completely saturate your tank"
that would take 620,807,533 bubbles

and at the rate that the bubbles are generated that would be
73.1 hours. You are right it would take a long time to COMPLETELY SATURATE the tank from a state COMPLETELY DEVOID OF O2.

But that is not the case, in reality the pump would just have to introduce more O2 than the organisms (fish, bacteria, frogs, craps, shrimp, whatever else) are using. We could deduce that Current Oxygen level = Given previous Level + (oxygen rate in- oxygen rate out) *time delta of previous to current time.
Given enough time to reach saturation (73 hours seems pretty close to the amount of time many fish keepers would test a tank for leaks), it could easily maintain saturation.


(note, I hope I do not sound defensive nor aggresive during this. I am enjoying this discussion and am glad to have input that is scientifically based. I do feel like I'm learning something here, hopefully others are as well)

 

[Bignose]

But, the biggest thing is that I estimated a minimum... the increasing oxygen in the water would decrease the mass transfer of oxygen out of the bubble. There is a sink in the water from that consumed by fish, plants, bacteria etc. But, it should reach a steady state. Since with increasing oxygen in the water it lowers the exchange exponentially:

N_act = N_org*((cb-cw)/cb)^n

where

N_act = actual gas exchange
N_org = what was calculated above with oxygen devoid water
cw = concentration of oxygen in water
cb = concentration of oxygen in bubble
n = exponent, since we are dealing with spheres, this is probably equal to 2

So, when the water is half saturated, only 1/4 of the mass transfer out of the bubble occurs.

So, now we want to know what the concentration after any time is. The amount transfered at any instant in time is a function of the immediate concentration. So, we have to integrate from 0 to T. As it is an exponential function it will take an infinite amount of time to reach 100% saturation, but we can calculate for any T what the current saturation is.

At 73 hours the water really is: 50.2% saturated with oxygen
At 100 hours: 58.0 %
At 500 hours: 87.3 %
At 1000 hours: 93.2 %

In fact, the water is not 99% saturated until 7223 hours. Or about 100 times as long as estimated when you take pure water. And, this assumes the water is perfectly mixed, which it usually is not. Unless you have some decent currents, there will be concentration gradients that will penalize this further.

Yes, you do not have to reach 100% saturation to keep your animals alive, but this is an incredible amount of time -- the surface agitation is a very significant part. The extra surface area means everything, and since it is a planar surface, the exponent in the above equation is 1/2 or 1, not 2, which is an extraordinary penalty.

Besides, after adding bio-spira you can add fish immediately (according to it instructions, anyway) you dont have to wait 73 or 7000 hours to saturate the water... the filter return splashes the surface. And, all the people who don't use air stones or wands and never report a problem. The bubbles do add some oxygen, but the dominant mechanism is the surface agitation.

 

[Apache]

OMG, y'all are toooooo technical for me! I have a headache from all the numbers... But, then again, that's why I teach art and not science/ maths!

All I know is, that we have a 30gal hex tank with a biowheel filter, and we only turn on the airstone every 3 days or so at night, and all the fish are doing just fine!