hi there, my first post so here goes...my daughter wanted to have fish for her chosen pet so we agreed...I have been the one to set it up and ultimately have to maintain it as shes only 8! anyway the tank we went for is a 40l tank and was left running for a fortnight before introducing 2 bog standard goldfish. the internal filter appears to be now struggling with the waste and the water has become bitty... the water was tested by our local aquatic centre and just shows signs of "newtank" with traces of amonia and nitrates and the ph was7.6 and was reccommended to do a wee water change. I did so and the fish seem okay but on occasions look lethargic but okay again.... I was wondering as its only a sponge filter and will take time to settle (is that cycling) for the good bacteria to get up to speed, or is te filter just not up to the job? it came with the tank so assumed it would be okay...anyway from the little research i've done external filters seem far superior... would you guys think thats the way to go?? if so which one?? ive seen so far 'fluval 106' or tertratec 600' seem to be the smallest for the 40l tank....any help would be appreciated thanks!!