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 Post subject: Use of venturi diffusor
PostPosted: Mon Dec 16, 2013 3:41 am 
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I installed a diffusor (Eheim type) working as a venturi pinciple on the outlet of my waterpump. This generates a very good aeration.

This diffusor produces a continuous background noise; although not exagerated (for us). My question is : does anybody know if noise in general (aeration pumps, filters, diffusors) is stressing our fish.

Reading some articles on the internet learned that studies have been conducted (University of Leiden in the Netherlands) on fish and they came to the conclusion certain noises (didn't notice the frequency and the intensity) could harm fish.

Does anybody (biologists among us?) knows more about this topic?


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PostPosted: Mon Dec 16, 2013 6:17 am 
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Hi Maanvis,

I have run recirculating systems for a long time in which I keep my discus and angels and some of the pumps I use make a constant low humming noise or sometimes they cause a vibration. I have not seen the fishes react badly to the humming, and I do not think that it is harmful. I would think that a vibration would not be good because fishes have a lateral line organ with which they sense vibrations and movement. I have found that my fishes tend to be jumpy in a system which there is a pump that is vibrating. So the question is whether your noise is not associated with a vibration and if it is, I would perhaps be careful.

What I am more worried about in your post is the fact that you are using a ventuari effect to introduce air into circulation. Such systems are well known to supersaturate water with air and to cause air embolisms in the gills and blood which can be lethal for the fishes. As a result I would be very careful with a ventuari as I have lost valuable fishes as a result of this in the past. I had an outlet pipe develop a fine crack through which air could enter the pipe and create a ventuari effect. The outlet was under the water surface when it entered the tank, but the ventuari was then jetting out finely dispersed air at the same time. Fishes can show bubbles under the slime layer in cases such as this, and some of the angelfishes in this tank developed these symptoms but two of them died as a result of what I assume were gill embolisms, this is well documented in the aquatic literature.

Kind regards,

Dirk

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PostPosted: Mon Dec 16, 2013 12:37 pm 
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Thanks Dirk. My device is a commercial diffusor from the brand EHEIM. I've been using it in the past in a larger tank with a bigger pump. In the tank I can observe a cloud of small air bubbles. I think these are not the result of oversaturation but simply the remaining of the air bubbles 'succed' into the water.

A friend of me working at the aquarium in a zoo told me they had once the issue with a leaking tube, allowing an air inlet. About 300 fishes died.

I don't fully understand that at atmosferic pressure, in water that is in movement, a gas can be in oversaturation for a long time. If the gas is under pressure, the solubility increases and when it turns back at atmosferic pressure, there is a real risk of oversaturation. In my case, with the pump I have, there is almost no increase of pressure and hence no increase in solubility.

Do you really think oversaturation can happen without expansion of the gas and in water that is in movement? If the answer is yes, I will eliminate them hoping my two pumps give enough circulation to provide the needed amount of oxygen.

Where I really fear for overstauration is when I apply a large waterchange (60-70%) with tap water which is under pressure.

In attachment a picture of the diffusor, just to be sure we taks about the same device.


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PostPosted: Tue Dec 17, 2013 3:25 am 
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I eliminated both diffusors from the pump outlets, although there were no issues. To me there is enough mouvement in the water to have saturation in oxygen. I will measure my redox regularly, can give an indication.

in the meanwhile, the sound of silence came back, as well in the tank as in the surrounding.

I also decided to stop with 60-70% waterchanges, as I'm using tapwater which is under pressure. I never had an issue with it, but I want to avoid any risk.

thanks for your comment Dirk.


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PostPosted: Tue Dec 17, 2013 1:32 pm 
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Hi Maanvis,

Firstly, I got the name wrong and it is of course the venturi effect and not the ventuari effect, getting old, you know....

Then I checked on Wikipedia because I remembered from the elementary physics that I studied about 40 years ago that the venturi effect is caused by changes that are brought about in the water pressure when you narrow the outlet as in your venturi and then because the water pressure is changed the air solubility is changed. Have a look at this, it explains this quite well. http://en.wikipedia.org/wiki/Venturi_effect

Then I think that when one has the leak on a pipe in which air is sucked in this forms very tiny bubbles and because the surface area of small bubbles is much greater than large bubbles, the water gets supersaturated, and this then may also add to the supersaturation.

Kind regards,

Dirk

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PostPosted: Wed Dec 18, 2013 3:45 am 
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I understand Dirk, my lessons of physics are also 40 years behind me. The venturi principle is based on Bernouilli's law (for liquids). But what I wanted to say is that over- or supersaturation is a thermodynamic unstable equilibrium. As soon as a perturbation occurs, the gas will leave the liquid (this is what happens with the bubble gas desease). When there is enough mouvement, and this is the case at the outlet of a pump, the gas should (normally) leave the liquid.

I understand supersaturation can occur when coming from a situation where gases are more soluble to a situation where they are less soluble. For instance, coming from a high pressure (in tape water) to the aquarium (atm pressure) or coming from a low temperature to a higher temperature.

In a pump, the pressure in the water will increase and hence gas bubbles present at the inlet wil solubilize after passing through the pump. At the outlet, water is coming at atmosferic pressure again and the gas is in oversaturation. So I think the risk is higher when the addition of air is done before the pump.

If there is no mouvement in the water, we can understand that locally there might remain an unstable equilibrium if there is a source of gases (e.g. plants in a pond).

Whatever, I took your advice and eliminated the diffusors. I heared from several people this can occur, so it can happen. I just don't fully understand.

I would also pay attention during large waterchanges with tape water. There is also mouvement in the water and you see of course the bubbles sticking on everything in the tank, but a danger for supersaturation is not excluded neither in this case.


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PostPosted: Wed Dec 18, 2013 12:34 pm 
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Sorry, it was 30 years ago. Feels much better :D


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PostPosted: Wed Dec 18, 2013 8:54 pm 
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Hi Maanvis,

Ok, I fully agree with what you write.

You are of course perfectly correct that cold tapwater added to a warmer aquarium can also lead to supersaturation. Particularly with the cold temperatures that you are experiencing now this can be a serious problem. I am in the fortunate position that I live in an area that never freezes in winter and the tap water seldom goes below 12-15 C, so I don't have this problem really.

With regard to your physics lessons being 30 years old, I fear that my physics lessons ARE 40 years old, the years are rolling by, and I cannot stop them....

Kind regards,

Dirk

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PostPosted: Thu Dec 19, 2013 3:30 am 
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Hello,

It looks the behaviour of the group (5 Santa Isabels, 2 scalare & 1 leopoldi in a 350l tank) is quite different. Before, the fish were more nervous and two of them were defending a corner. Since I took away the diffusor, I see a homogeneous group swimming toghether and more slowly. No more struggling.

Are they reacting to a changement? Or was the noise or the airbubbles making them more active or nerveous?

Regarding the behaviour of the fish, I saw a significative changement when I transferred the group from a 700l tank to the 350l tank were they live in now. Although they have to live in a smaller volume, there is much less agressivity among the group.


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PostPosted: Fri Dec 20, 2013 1:48 am 
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maanvis wrote:
Hello,

It looks the behaviour of the group (5 Santa Isabels, 2 scalare & 1 leopoldi in a 350l tank) is quite different. Before, the fish were more nervous and two of them were defending a corner. Since I took away the diffusor, I see a homogeneous group swimming toghether and more slowly. No more struggling.

Are they reacting to a changement? Or was the noise or the airbubbles making them more active or nerveous?

Regarding the behaviour of the fish, I saw a significative changement when I transferred the group from a 700l tank to the 350l tank were they live in now. Although they have to live in a smaller volume, there is much less agressivity among the group.


Interesting observations Maanvis. A few months ago I modified the filtration system on the aquarium where I presently keep a group of 15 altums (18+ months old). This tank is 225 gallons (plus 55 gallon sump) and I eliminated the sump and magnetic drive pump, now relying solely on air powered filtration through sponges and diffusers. I have 6 Hydro Sponge (Model V) that supposedly filter up to 125 gallons each, all is powered by a commercial linear piston pump and gang valves.

I also ran a direct line from my semi-commercial RO (GE Merlin) to the tank and installed a solenoid valve which is controlled by a dial type analog timer. At 4pm each day, new RO water enters automatically into the tank for one hour providing around 25 new gallons. This accounts to a change of about 175 gallons weekly. Since my tank is in the garage, and my sump pump is disconnected, the old water mix simply overflows out of the sump. The flat water rate helps.

pH is maintaining stable at about 6.0 and the water is very soft. My substrate helps provide some minimal hardness and my aged membranes (over 1 year old) also allows some measurable TDS, but I provide as much vitamins and minerals as I reasonably can through commercial foods and a broad range of frozen and fresh foods.

I am working on a way to precondition the incoming RO water with catappa, red bush tea and peat (this would imply a preconditioning chamber or drum containing these products). But this would mostly be interesting for breeding of wild caught specimens.

Most important ... since I made the change, the fish are eating much better, they look much more relaxed and school more naturally.

Ed

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PostPosted: Tue Dec 31, 2013 12:35 am 
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Since I took away both diffusors, it looked like the fish were breathing slightly faster (without having difficulties). I measured ORP, which was 290 mV with simple water circulation, while it was 350 mV with diffusors. Since nothing changed in the environment (same temperature, same food and same amount, etc...). The chemical or biological demand in oxygen should the same, what should mean that the water isn't saturated in oxygen without the diffusors. I decided to use them again.


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