I have 50 tanks and do all my changes from the tap. I do 70 to 80% changes with no ill effects on the fish. All my fish are healthy and spawn all the time. The only fish I have not been able to get to spawn that I have tried has been S. angelicus and since no one else does I do not feel bad. People in general think that fish are more delicate then they are. While I am not advocating this for the begineer once you have some knowledge and experience you will see what I mean. I have a 110 gallon planted tank in my living room on which I always change about 80% of the water. It never fails that after each of these changes (done bi-weekly) the angels, cories, and kribs will spawn. The rainbows spawn daily but much more intensly in the few days following the water change. Suffice it too say that so long as your tap water is not terribly wonky you will have no trouble doing changes straight from the tap. This obviously does not apply if you are altering your water parameters for some of the more difficult fish like discus or apistos. Just my two cents, what works for me may not work for you. If what you are doing works, as the saying goes, if it works don't fix it. You do have to be careful if you are changing a lot of water at once as the temperature will fluctuate a bit. If you are lucky enough to be able to use a laundry tub with a long spout on it you can stick a sticky digital thermometer to it and it will tell you the temp of the water coming out. I always make the water coming in a few degrees warmer as I think fish are more easily able to deal with a rise then a fall in temperature. Nothing to back that up except for personal observations. I do put cooler water in however when I want cories to spawn but that is a whole different topic.