Sorry to say that there really is no way to avoid a large cloud in your tank if you need to add sand. I would add a cup or 2 and let it settle out and then repeat. The PVC
works pretty good at minimizing the floating particles but the only thing that really is effective is time. I added to the bottom of my over flow about 2 months ago and I had a cloud for a day and a half. Considering the bottom of the overflow is only 6" X 6" and I only have the sand 4" deep you can imagine the mess you will have if you add all your sand at once. A small, short term cloud will not have a big effect on you inhabitants but I lost a couple of damsels during my main tank sand fill in which I added pretty much all at once. That cloud lasted over a week.