This is an article that details how to make a relatively inexpensive, highly effective, air driven biological filter. These filters are basically just a bigger, better and uglier version of the common plastic box corner filter available at your local pet store, and for many of the people who read this it will be common knowledge, so it is more for the benefit of newcomers to the hobby, or perhaps those hobbyists about to go from one or two tanks to a room full of them. I take no credit whatsoever for the information here, as most of it was gleaned from far more experienced hobbyists than myself, I am merely presenting it for the benefit of those that do not have access to such information. They are extremely unattractive in appearance and therefore best suited to fry tanks and breeding tanks, where aesthetic appeal is not the goal.
This filter works on the biological filtration principal, otherwise known as "the nitrite cycle." I will assume that the readers are familiar with this, however, if you were not, it would be a good idea to do some more research on it. The filter uses air to move water through the filter media. The filter media houses the denitrifying bacteria that is the essential to removing biological waste from the water. The filter can be built for a very low cost, and are therefore a great option to be used in a fishroom with many tanks.
The following parts can be obtained in a supermarket, pet store and around the house (or in the junk bucket in your fishroom):
- plastic container (approx 1 - 3 litres)
- plastic lid to suit
- air stone cylinder type
- 12" length of airline tube
- airline tube connector or in line tap
- 6" length of tube ¾ inch to 1 inch diameter (electrical conduit or UGF uplift tubes are best)
- empty plastic coke or OJ bottle
- lot of gravel/filter media
The following tools will be needed:
- electric drill (battery or mains, I use one of each)
- 1/8 approx. drill bit1 x ¼ approx. drill bit
- ¾" - 1 inch diameter hole saw
- sharp knife
- pair of tough scissors
I've got it down to about 5 filters in an hour, but I'm a slow poke.
I use a 1-litter plastic food container, you can also use Ice Cream containers, margarine containers etc. Make sure the lid is on the container if doing one filter (multiples you may stack the lids). Using the 1" hole saw drill a hole bang smack in the middle of the lid (most containers have a nib marking the centre of the lid). Next, change the drill bit to the ¼" and drill many holes around the lid (see top view) until it looks like Swiss cheese. Remove any plastic tails created by the drilling process with your fingers or the knife. The lid is now finished, so put it aside.
Take the empty coke or juice bottle (I have found two-liter coke bottles the best with a 1-liter container). Cut the bottom inch and a half off the bottle off with the scissors and make sure that it fits flat (turned upside down) inside the container. Throw the rest of the bottle away. Try and even up the cut bottom as much as possible to ensure it sits flat on the bottom of the container. Take the hole saw and again drill a hole bang smack in the middle of the bottom of the bottle. Note: The bottoms of the bottles are generally thicker than the rest of the bottle, beware as the hole saw will grab and spin it around if you push too hard. Change drills to the 1/8" bit and drill holes all around the bottle base so it too looks like Swiss cheese.
Place the bottle base upside down in the container and fit the 6" length of UGF uplift tube in the hole. Try and match the size of the hole to the tube so it fits as snug as possible. If the hole is too small for the tube, you can cut slits in the bottom of the tube and squeeze it together to make it fit. If the hole is slightly larger and tube slips through, you can make a cut in either side of the tube that allows you to fold out a flap of plastic to stop the tube pushing through. Drill a ¼" hole in the "top" end of the tube to feed airline tube through.
Take all components to the tap and rinse them thoroughly removing all plastic shavings, stickers/labels, ice cream, glue residues etc. Put coke bottle base upside down in container and fit chimney tube. Fill container with your choice of filter media. Feed the start of the airline through the ¼" hole in the top of the tube, pull it out the top and attach the air stone, then poke it back down the tube. Pull on the airline so there is no kinks in it. Squeeze the lid of the container over the chimney tube and airline and close it on the container. Fit a tap or airline adapter to the loose end of the airline. (The use of the adapter makes it easy to disconnect the filter and remove it from the tank so you don't have to remove yards of airline tube with the filter when you remove it.).
Put the filter in a fish tank (be careful not to squash any fish) and attach the air line. The blue arrows in the picture show the water flow through the filter. That's it!! You're done!! Cleaning Take the lid off, dump the media in a bucket and rinse (I use a pasta strainer to rinse it). Wipe out the filter and lid with a "fish only" sponge, re-assemble and place back in the tank.
Fry can actually get inside the filters through the holes in the lid. This is no problem as the fry will live happily in there for weeks (I've proved it) because a lot of food is pulled into the filter at feeding time. Smarter fry actually us it as a hiding spot and for this reason you may wish to leave an inch gap between the lid and the top of the filter media Anything can be used as a media. Coarse gravel is good. I use shell grit to help buffer the alkaline water for my Tanganyikan cichlids. Filter wool, cushion wadding and ceramic noodles also go well. If the media is too fine, the water flow will be greatly reduced. For this reason I grade my shell grit by sifting it through a pasta strainer. I keep 6 or so in a small 2ft tank to keep them "charged up" with bacteria ready to go. It's handy to keep spares so you can swap them when you want, and you can get around to cleaning them later whenever you feel like it. I have found two 1 litre filters more than adequate for a 40G tank full of fry To cycle a new tank, take two old filters and put them in the new water and this will cycle a new tank in a few days (always test with nitrite kit before adding fish, and re test in a days time).These filters can also be made without the use of the base, but I like the idea of having a bit of water under the chimney, it seems to help the water flow?
In terms of the air flow from the air stone, the faster the better, in my opinion. If you don't have or don't want to use air stones, you can tie the end of the air tube in a knot and poke holes in it with a needle heated over a candle. This is good for high volume fishroom pumps that don't have much pressure behind them. Coke bottles are generally the best to use for the base as orange juice doesn't mix that well with bourbon. Any additional information, please feel free to contact me.