well here are my "specs"..

tank= 4ftlong, 2ft high, 1ft deep but bowfronted and comes out to 1 1/2ft deep.

260 litre

current fish 1x7 inch red oscar, 1x3 inch albino oscar, 1x12 inch pleco, 1 apple snail.

current filteration fluvel 404 canister filter and a standard built in filter.

heres what i was thinking. i know my tank is a tiny little bit small for the amount of fish:S but i think i currently have good filteration. what i was thinking of doing was pulling the insides of the standard filter out and putting another canister filter in like the fluvel 404!

my quistion basicly is..do you think this is woth doing?

i can not get a bigger tank for many reasons, mainy due to space in my little flat so it is out of the question:(

Extra filtration never hurts. I personally would leave the internal filter functional and running. It means that you will always have that filter as backup if something were to go wrong with a couple of your filters, you never know what can happen.

The only problem you might have is feeding the pipe work in for another canister filter with the internal filter in situ.

i did what you said about putting an extra blue sponge in my filter. it now has 2 brown pices at the bottom then 3 blue pieces then the white piece so it is a pretty good filter i think. it would be a little hard putting a new canister in with the standart filter in place but it would just mean getting some adaptors to bend the piping a little. i will have a look and if i can pick one up for a good price i will do it.

my air pump wasnt that good before but i have just got a new one with a air curtain going along the back of the tank and the oscars are allready playing in it which looks pretty kool lol.

i had no look with giving the pleco away and have decided to keep him for a little while as i do like him .

you probably have increased the biological filtration by quite a lot by adding the new sponge. I actually think you're doing really well with the filtration you've got at the moment. The easiest way to determine how efficient your tank is with the canister is how quickly the internal filter gets dirty.

what part of the internal filter? the white part or the blue part getting dirty? or both? am i right in saying that i have to throw away the white piece every week and replace with a new one? also what are the 2 brown pieces at the bottom of my filter doing?