Filtration for discus tanks

[Mugwump]

Dennis, can you describe the 'Jetlifter? tubes '....I can't remember what they look like,,they allow for more water flow, without the bubbles,etc...

[BallAquatics]

Dennis, can you describe the 'Jetlifter? tubes '....

With just a modest air supply, these things really move some water...

While Jetlifters come in several different shapes and sizes, they basically all work the same.  Under the dark grey airline attachment point the lift tube has several rows of small holes.  These allow for the air to travel up the wall of the lift tube leaving the center of the tube completely unobstructed.  This makes for a great transport of water.



I have about a half dozen of these in daily operation.  They are easy to clean and seem to be very durable, I've only had mine for a couple of years now.  If I could afford it, I'd have them on all my tanks!

Dennis

[Mugwump]

Ah, yes..the holes....I remember the demo at the ACA last year....looked interesting..but a bit pricey....thanks, good picks.
Isn't that air tube connecting piece similar to the ones on UGF's..??....looks familiar....?

[PaulineMi]

Regarding "airlift" for those of us new to fully understanding what's going on. This is from an article by Kenneth Thurston.

Airlift can be readily understood by considering what happens when a bubble is released in water below the surface. The first obvious observation is that the bubble quickly rises to the surface. What isn't so obvious is the fact that as the bubble rises; it does so faster than the water can slip around the bubble. So there is a small column of water that is being pushed ahead of the bubble, some of which is actually pushed above the surface. So what about the water that does slip around the bubble? Well if we use a whole lot of bubbles and surround them with a tube (or use a narrow tube with few large bubbles), the water that slips past a bubble either lands on the column being pushed by the next bubble, or it has trouble getting past the bubble due to the walls of the tube. So even though it isn't obvious to the viewer, an airlift is capable of moving very large quantities of water.

When the airlift principle is applied to under gravel filters, sponge filters, and inside box filters you have to realize that there's a little more to the story. The water is pushed into the filter by the water pressure at depth. The airlift then moves the water out of the filter. The combination of water pressure at depth and airlift forms an effective water pump mechanism. Even though this is a very effective water pump mechanism, power heads have become an enormously popular replacement for air pumps because their effect is more readily observed. Unfortunately they don't aerate as well as an airlift. As far as aeration is concerned, there is a frequent misconception that in an airlift, the bubbles mix with the water to create aeration. Aeration actually takes place at the surface. If you observe an aquarium that has a few air stones or airlifts running in it, you'll notice waves that agitate the surface with waves that propagate through out the aquarium. It's this surface agitation that improves the aeration, not the mixing of the bubbles with the water.

[BallAquatics]

Isn't that air tube connecting piece similar to the ones on UGF's..??....looks familiar....?

I think it's custom made to fit the jetlifter.  It fits very snug to the lift tube at the top and bottom, but the middle section is open and fills with air.  This middle section matches up with the rows of holes in the lift tube....  I wonder how much effort would be required to try and DIY some of these???

I believe that my DIY lift tubes move almost the same amount of water, but the air stones in them need to to be regularly replaced at an added expense every couple of months.

Dennis

[Mugwump]

Isn't that air tube connecting piece similar to the ones on UGF's..??....looks familiar....?

I think it's custom made to fit the jetlifter.  It fits very snug to the lift tube at the top and bottom, but the middle section is open and fills with air.  This middle section matches up with the rows of holes in the lift tube....  I wonder how much effort would be required to try and DIY some of these???

I believe that my DIY lift tubes move almost the same amount of water, but the air stones in them need to to be regularly replaced at an added expense every couple of months.

Dennis

Have you tried it without the air stones??..bigger bubbles move water better, especially when confined to a tube...I would think??...that's why I was asking, perhaps I can rig a smaller one for a first try...

[BallAquatics]

Have you tried it without the air stones??

Over the past 20 years I've made more DIY filters than you can shake a stick at!  lol lol lol.  Here's one of my DIY's using small tubing without air stones from several years back ==>

http://www.danionins.com/articles/diy-foam-filter.html

Through trial & error I have found over the years that if you want to move LOTS of water you need more bubbles!!!   

Dennis

[BillT]

There are two different mechanisms involved in airlift function. One is the bubbles pushing up the water above them. The other mechanism works on the reduced density of the water in the lift tube vs. the rest of the water in the tank. The bubbles make the water in the lift tube less dense and it rises by the same mechanism that keeps boats afloat.
Both these mechanisms work in lift tubes.

Aeration is basically gas exchange across an air water interface, oxygen into the water carbon dioxide out. This will occur at the surface of the tank and at the surface of the bubbles moving through the water in the airlift. The amount of gas exchange will be proportional to the amount of surface area in the bubbles and tank surface.

In addition the amount of gas exchange will be proportional to the difference in the amount of the particular gases (such as oxygen or carbon dioxide) in the water right next to the surface and in the air. As gas from the air is dissolved in the water, the concentration of that gas will increase in the water, thereby reducing the driving force that pushes the gas into the water. The gas dissolved in the water will diffuse away from the surface, once again lowering the concentration of the dissolved gas at the water's surface, so that gas exchange can speed up. However, diffucing is a relatively slow process. Turbulence in the water (such as from aeration) will will quickly dissipate the dissolved gas build-up and therefore maintain a more rapid gas exchange. This will happen around raising bubbles or at the surface of water that is agitated.

[PaulineMi]

. The bubbles make the water in the lift tube less dense .

Is it the fact that there are bubbles in the lift tube replacing water that makes "the water in the lift tube less dense" or does it have something to do with a gas exchange of some type?

[BillT]

Is it the fact that there are bubbles in the lift tube replacing water that makes "the water in the lift tube less dense" or does it have something to do with a gas exchange of some type?

To a large extent it is the bubbles that reduce the overall density of the volume of the water air mixture compared with the water without the bubbles.

Density of air dissolved in water; an interesting question I had not considered: there are at least two possibilities:
1) Reduced density: The air molecules in the water take up space of the water molecules, pushing them out of the way. This might make the water a bit less dense if the weight of the gas molecules per the volume (weight/volume = density) they displaced the water molecules from is less than the density of the water molecules alone.
2) Not reduced density: The opposite argument. The dissolved air molecules do not displace a greater weight of water mlecules than the weight of the gas molecules dissolved in the water.

If the water with air dissolved in it is less dense it would add to the air lift effect but it is unlikely to have as large effect as either the reduced density of a water/bubble mixture or of the effect of raising bubbles moving through the water.

Another air lift effect is that large bubbles in a small diameter tube will very effectively push the water up of they completely span the diameter of the tube. In this situation the large bubbles act like mechanical pistons.

Related situation is a carbonated beverage. A huge amount of CO_{2 is dissolved in the water. If that gas were to come out of solution as bubbles and collected, it would make a large volume of gas compared to the original volume of the water with the gas dissolved. These guys http://www.science-house.org/index.php/component/content/article/142-how-much-carbon-dioxide-is-in-a-bottle-of-soda claim it is about 4 times the volume of the water and dissolved gas. In that case the water-dissolved gas mixture should be heavier because of the gas molecules in the water. This may not be the case with other gasses because CO2 of the charged nature of water and the things CO2 does in water to form related charged molecules like carbonates. Charged molecules get along better with water molecules and pack more densely.}