Ok so the questions:
1. water flow - how much water movement do fish actually like? they dont want to be fighting a current all the time obviously....
As long as they arnt getting blown around then they should be fine. Most of the fish we stock come from rivers or lakes & they all have moving water. So the fish are quite happpy to be swimming in a current.
Ive just been home for lunch, did a 20% water change and altered the angle of the pump output, i must say they seemed to actually enjoy the current, especially the tetra, they sat there fighting it on purpose! I guess its like being on a tread-mill in the house if you cant get out.....
by the way, as its a big amount of water to change, im pre-warming the water to what feels about the same as the tank to avoid big temperature variations, i assume this is good practice? (i have a hot water on demand water heater so its fresh water, not from a immersion heater)