Hi macbella, I answered your post in the other thread. In short, what I said there was that there is no need at all to change 100% of the water; this is actually harmful rather than helpful. All you really need to do is take out 30% of the water, while the fish is still swimming in his home, and then change that with the same amount of fresh water. Do this on a regular basis, and he will be a lot less stressed than if you do 100% of the water on a less regular basis, because changing all the water at once can shock him into getting very sick, and destroy good bacteria in the gravel. Cleaning the tank is not really about getting all the dirt you can see out of the tank; it's about exchanging some of the impurities in the water that you *can't* see. These are called ammonia nitrite and nitrates (you can test for these, or bring in a water sample to your pet store, who will usually test it for you for free), and are explained in the link I posted on the other thread. Even crystal clear water can have these! So it's more just about diluting them down on a regular basis. Read the other post for more links; I hope that my article, Bringing Home Your First Betta, helps you out. Good luck and happy new year.