Reposting filter instructions:


As I said, you may already have everything you need for this, it is an
internal biofilter and with any luck you can camouflage it behind some
ornament or even get creative and using aquarium sealant, glue some pretty
rocks (real or fake) to it, to make it look like something else.

You will need: a power head (any power head), a quart size plastic jar
with lid (a mayonnaise jar works really good), and any ceramic porous
filter media, or bioballs, or even coarse open cell sponge cut into cubes.
I use the ceramic media. You will also need some basic tools.

Remove the power head base cover that normally goes into the undergravel
filter tube. Measure the base across. See if you can get a hole saw that
will have exactly the same diameter. If there is a hole saw shortage, you
will have to patiently cut out a hole in the lid of the jar by hand. Just
make sure it is a very tight fit, or else you will have water coming in
not through the filter, but through the opening right below the power
head, and you don't want it.

Take the jar, remove its label and remove the glue that held the label,
best with alcohol, so you don't spread any chemical stuff all over the
jar, also so you don't damage the jar itself. Mark some holes in couple of
rows somewhere around the bottom of the jar. They should be not larger
than 1/4 inch
in diameter, or at least small enough so the media won't fall out. Cut the
holes out carefully, the jar is kind of brittle and likes to crack.

Now snap the lid of the jar onto the power head's base. If the power head
comes with an o-ring, you can put the o-ring back on it to secure the lid
even better. Fill the jar with your favorite biofilter media, screw the
lid on and if you're using plain jar to hide it behind something, you may
use the sponge sleeve that fits Magnum 350 cartridge as a pre-filter. If
you decide to make an ornamental piece out of it, and just camouflage the
power head itself, you will probably have to do the maintenance more
often.

In Harold's tank, one is hidden behind a fake fossil rock, and another one
pretends to be a reef. Your imagination will set your limits. Most
important, the water quality is fabulous and Harold is one happy fish.

Love you all, - Maggie's Mom