Beta & tank cloudy

Question
Hi - my beta and his tank are "cloudy".  The first time I cleaned his tank, I cleaned about 3/4 of the water out.  After adding clean water to the tank, it was cloudy again.  So I removed him from the tank and completely cleaned the tank.  I emptied everything out, cleaned it and let it dry over night.  

The tank only stayed clear for one day or less.  What can I do...??

My other two beta tanks are still clear from being cleaned by removing only 3/4 of the water and returning clean water the to their tank.  Thanks!!!

Answer
Lori,                                                        I know this is going to sound wierd , but sometimes its the rocks. I have run across t5his prob a couple of times and it was a bad batch of rocks. Trying changing the rocks and see what happens. Get Back to me , Tina