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I needed a gentle filter for my quarantine tank and had lots of stuff laying around, so it was time to DIY!

Materials :

- Bottle: Can be any plastic bottle on earth
- Tube: I used the handle of dish sponge thingy that was about to be thrown out. Any plastic tube is fine.
- Media: Gravel, sponges, floss, ceramics, LEGOs, diamonds, etc. It's all good.
- Air Stone: Should fit inside the tube.
- Air Tubing
- Air Pump
- Check Valve: Optional (but not really)

Tools:

-
Drill
- Saw (Hack- or other variety. I used a bread knife.)
- Hobby knife

Step 1: Prep the Lid

I picked an old Nalgene bottle for this project because:

1. It's study
2. It has a relatively large capacity (1 liter)
3. It has a wide mouth for easy servicing.

The first step is to prep the lid for drilling. The lid comes with a swivel connector on the top that keeps it attached to the neck of the bottle. Luckily this snapped right off with a light tug; I'm not sure if this was due to the bottle's age or if the connection is just flimsy. Still, I definitely expected it to put up more of a fight.

Step 2: Drill the Lid, Insert Your Tube Into the Hole

Innuendo fully intended.

This step will be easy for those who have a carving drill bit. I used a combination of a 5/8th bit, a sanding bit, a SA knife and brute force. Make sure you don't make the hole larger than the outside diameter of the tube; the extra space between the tube and the lid will allow water to bypass your media, rendering it less effective. So get it tight, get it right.

Here's my Nalgene lid with the handled kitchen sponge tube. Why is there an extra hole in the lid?! Stay tuned...

Step 3: Drill the Bottle

Next, drill some holes near the bottom of the bottle. This is where the water will enter the filter, so you can decide on the quanitity, size, and position of the holes. You want them to be off the bottom so they don't get blocked by the tank substrate, but not too high since the area between the holes and the bottom is essentially dead space (the air stone will draw water upwards inside the bottle.

I put my holes about a half inch off the bottom and at 1 inch intervals.

Step 4: Add the Air Stone

The original plan was to suspend the air stone inside the tube. Problem was: what would keep it in place?

Enter the aforementioned extra hole in the lid! I passed the airline tubing through this hole and then connected the air stone and placed it inside the tube. Ta-da! Stays perfectly in place. 

A note on the position of the air stone: You basically want it to be right at the bottom of the tube to maximize the water lifting action generated by the bubbles. So not at the middle or top of the tube. And definitely not beneath the lid where the bubbles will just accumulate inside the bottle.

(The air stone in my picture is actually a bit too high... so do as I say, not as I do.)

Step 5: Put It All Together

Finally, insert the media of your choice, screw on the lid, and you're done! Remember, the water will flow from the bottom to the top, so put the coarser media below the finer stuff.

Mine has plain black gravel and filter floss.

Step 6: The Tower in Action!

Connect the airline tubing to an air pump with a check valve and you're in business!

Here's the filter seeding healthy bacteria in my main tank. Hope you enjoyed this Instructable, and feel free to ask questions or leave comments!
<p>Did this for my fry with a small as hell vitamin bottle, since they are to small to keep with my other fish, and I didn't have an extra pump-filter... Thanks!</p>
<p>Can I use Activated Carbons instead of stones used from Water purifier...</p>
<p>Stilly question, but what's an air stone? When I googled all I got was gardening stones.</p>
<p>its the stone that is on the end of an aquarium air pump</p><p>https://thegirlwithfish.files.wordpress.com/2011/01/aquarium-air-pump.jpg</p>
<p>cool dude...will this make your aquarium clear?</p>
<p>I Made a smaller version of this with a vitamin bottle. Its a great concept.</p>
im thinking of trying this
Hmmmm, nice.

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