Honestly... I NEVER do waterchanges haha, the last one i did was when we moved house, 2/3 months ago.
Allthough im going to try and do one weekly now, or MINIMUM every 2 weeks.
Its just coz this one is hard to do waterchanges with, my new tank will have a hole in the back about 1/4 from teh top with a valve and hose connector, as well as a plumbed return line, so all you have to do is clip on 2 hoses, open the valve and turn on a pump = Waterchange done. :)