# Sponge filters: Short sponge, or short lift tube?



## Robanada (Jan 16, 2010)

tl,dr: is it better to cut a sponge filter's lift tube, to cut the sponge, or to compress the sponge?

Hey guys, I bought a Hagen Elite Sponge Filter from my LFS, because it was all that they carried, and I was eager to get started (and couldn't wait for an ATI Hydrosponge in the mail). Unfortunately, it's not possible to put an airstone into this particular unit, so the bubbles are large, make lots of noise, and splash a bunch.

I ended up taking the thing apart:



I removed all the 90 degree joint pieces, and tried to reconstruct what I thought the ATI sponges looked like. 



I rain the air tube through the lift tube, and put an airstone on the end. In the "final version" (after I took pictures), I put a little cone over the airstone to channel all of the bubbles into the lift tube.



The airstone was inserted into the top of the sponge (remember that in the final version, there was a cone connecting the top of the sponge to the lift tube, with the airstone inside).




*But then I ran into my problem: It was too tall!* (left side of following pic)


[Color key: blue = water level/air line, red = lift tube/bubble cone, yellow = airstone, black = sponge, green = substrate]

So now my problem is: do I cut the lift tube down, thus reducing the flow/lift in the filter (furthest right in pic)? Or do I cut the sponge down, thus reducing the total surface area? 

Right now, I've used the suction cups on the lift tube to squish the sponge at the bottom of the tank (middle in pic). Is this even a problem? The surface area should be the same for bacteria, but maybe since the compressed sponge would be denser, the water flux through the sponge would be reduced. Is there a way to check flow rate in these sponge filters? 

What would you guys recommend doing?


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## k19smith (Aug 19, 2011)

Did it fit originally? If so I would just get a (I can't remember the name of it) goes in line with your air line tubing and controls the air flow it's only $4 or so, even walmart has them. How big is the tank how big is the sponge rated for if you cut the sponge your going to change that. You can look up do it your self sponge filters and probably make something better. I don't figure you want the sponge squished. Hope this helps.


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## Robanada (Jan 16, 2010)

Yes, it fit originally, but only because the sponge was mounted at a 90 degree angle. I removed the 90 degree piece because it would not allow me to place an airstone in the setup. The air pump came with a valve, which I tried inserting into the line. No matter how much I choked it, the bubbles were still very large- just less frequent. The only exception was when it was VERY restricted, I could get a slow trickle of small bubbles- but the lift generated by them is nothing like the lift generated with the airstone that I have now. 

This sponge filter is not my primary filter in the tank. This DIY tank is oddly shaped, specific for this application (it would take a LOT of text to explain- I'll make a thread for it when my tank is complete), and as such it only has a 4 inch space in the back for a HOB filter. The only HOB filter I could find that would fit was for a 3 gal, but my tank is a 5 gal. So I decided to use a sponge filter for supplemental filtration. I'm pretty sure it's rated at 10-20 gal, but I'm not positive. In any case- I'm not terribly worried about losing filtering capacity. 

Thanks for the reply


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