I've got a question about taking care of a Betta fish?

You can change more than 20% of the water if you want, with 50% being a common limit for a single change. There are also electric gravel vacs that just clean the gravel without removing the water.

http://www.google.com/shopping/product/15071623079...

Also, to drain the water more slowly you can get a smaller hose to restrict the flow, or even kink a larger hose to restrict the speed the water flows out. The vacuum rate doesn't matter on the tube size, the flow of water is all in the hose size. You can get an adapter to connect the larger diameter hose to a smaller diameter, or even add a ball valve to restrict flow (or pinch the hose, or tie a knot)

You do not want to move the fish and over clean.

You need to siphon out the gravel as well. I place my siphon on top of/in the gravel and let it suck out the nasties :) But you do need to be cleaning the ornaments. I do a VERY mild bleach bath when I do a big change. Normally I end up doing a 40-50% change every 2-3 weeks (i'll get criticism for this but whatever). Make sure you are offering him flakes and/or pellets as well. They need a well rounded diet. If he refuses those, you can try to put a piece of lettuce in and hopefully he will eat that (organic ONLY).

put him in another tank with the same water and deep clean the tank, rocks, and ornaments to prevent ammonia. you should feed your betta pellets as well. it gives them their nutrients and color. when you stir the gravel, get a net and catch all the debris that is flying around. then clean the net after use. Hope this helps.

A 5 gallon tank seems a bit excessive for just a Betta.

Our Betta is in a bowl that contains about 3 cups of water and when we change it, we put him in a cup, change the water and dump him back in. For thorough cleanings, I'd suggest scooping him out though.

take out the bigger things in the tank, stir up the substrate a little then clean, or try a different vacume

ignore crb, they are just trolling..