Yes, you have to rinse it out well. I just used a 1/2G koolaid container, and put some in and rinsed while stirring the sand around, then when the water that was overflowing looks clear, then I added it to the tank. Took a while, but was well worth it. Then, when adding the water, take a large plate and turn it updside down in the tank, and run the water over it slow at first, but when the water get's a little depth, you can turn up the water pressure and fill it up. It will still get a little cloudy, so if you did a 75% PWC, it will clear the water up a bit. Then, don't run the filter for a couple hours, it should clear up fairly quick. Then add the filter.