It's not often I add sand to a tank anymore, but since I had to add some pool filter sand to the 125, I thought I would take some pictures. How many times do you have to wash the sand? As many times as it takes. I wash about 10-15 lbs at a time, which is about my fingers length in the bucket. The first picture is after the third wash (when I decided to chronicle this). And each picture after is at the finish of each successive wash. A wash consists of filling the bucket with water while churning the sand with my hand. After the 10th wash, I could see my hand on the sand. THAT is when it is clean enough to be added without clouding the tank.