I voted for 30-50% weekly as that's the nearest I think. I have a 110 litre and I drain 30 litres on average but if it's really grubby I aim for a 50% change. I also add plant furtilizer every week after my water change
I tested before my last water change and it was no worse than what came out of the tap. I'd actually been feeding more than usual since the water change before too. Not because I made a decision to, just because I didn't keep forgetting to feed them each night
I aim for 40% each week, but most normally it is every 10 days.
A friend in work has a 240L hexagonal tank, pretty heavily stocked with fully grown Angel fish...i spoke with him about 3/4 weeks ago and he said he hasn't changed any water in 4/5 months
I think a sample population of 65 in this poll is adequate to represent most peoples water changing regimes, thanks everyone for satisfying my thirst for knowledge