I have a 200L tank for my turtle ATM. He is like 12cm long. I have 700L of filtration. I do
Possibly 20% 2x a week. When I siphon I syphon out the gunk. Water is crystal clear no algae ammonia 0ppm nitrites 0ppm nitrates <5ppm. I also believe you don't need to do 100% every single week. Maybe only if I go away for 1 month on holiday I will do a 90%+ . I know lots of people that have turtles and none of them do 100%. And if all of the water suddenly changes temp the bacteria will die.