:blush: Yes, well …
I fill mine up every second week app. – I very rarely take any water out. But it seems the water evaporate down quite a bit for me, so when I fill up, its probably about 2-3 liters.
BUT I rather freqently make total changeovers. This is because in most tanks (all 12 liters) theres fry growing up, and at some point I need to take these out.
Also I admit that my tanks ends up getting rather overgrown and leaves, peat and so forth deteriorate, – so with most tanks probably every 5-6 months theres a whole changeover.
I also sometimes, when starting a new tank, starts out with just half a tank ( 6 liter) and then slowly fill it up untill its full.