I used to change the water over 70% at least once every week and was told by a trusted pet shop owner to scale it down to 25%, 30% at most because of the drastic change in water parameters. The best thing, she says, is to change it about 10% a day. Of course that is probably impractical for most people. However, I gave it a try vacuuming the tank water into a 4 gal bucket using a large syphon, de-chlorinate the bucket with fresh water, and dumping it into the tank, then cleaning up. The timer said it took me 6 minutes. Since I have two 75 gal tanks, that's about 12 minutes/day. Make sure you get a bucket with a spout that sticks out because you'll find it difficult to pour the water into the tank without making a wet mess otherwise.

I've been doing this for 2 weeks now and I noticed the dorsal fins on my oscars are straight up and they are a LOT more lively. My community tank the neons and other tetras are playing with each other more and overall a lot more lively. So the change is about 5% a day but I think its smallness helps stabilize yet clean their environment. Has anyone of you ever tried this? Wow, I wish I did this when I first started.

I suppose a constant supply of fresh water is good for any aquatic animal. Whether or not your fish are any healthier than somebody who only does one water change week is difficult to determine. I suppose the best way of doing it is to set up two tanks exactly the same with exactly the same fish in and do an experiment and see how you get on. Doing a water change on a relatively small tank isn't going to take me long. However, when you've got a big tank, it could be a bit more tedious. I think it's best just to be sensible and don't overstock and your water parameters should be stable for the week. Obviously, your nitrate levels will rise slowly as long as they are kept reasonably low, your fish should be okay.