Keep in mind that everything you read on this board is an opinion. Everything you read is also fact. The things that people do, by in large are true and accurate to what they write, as are the results. The problem is, space, time and writing talent limit how much detail people can put into their responses. Vital details are left out, and those details may or may not pertain to your circumstances and results. I would suggest you post, watch the answers then to searches on your topic. When you find a lot of different answers you will be able to get a feel for what will apply to your situation. It takes a while, but patience is critical for this hobby.
I read a few posts that said Southdown didn't have to be rinsed also, but then re-read some of the more senior posts and responses from people like Mr. Salty, Broomer5 etc. and saw reccommendations to wash.
I took a 5 gallon bucket and filled half of it with SD then poured water into it. Three days later when it finally settled, I noticed the film on top of the H20, then I drizzled some new water into the bucket, when I saw the clouds reappear like silt, I decided to rinse it.
I took my 50 lb bag of SD and filled half of my 5 gallon bucket at a time and rinsed each bucket for about 20 minutes. It took me the better part of an afternoon, but I think it was the right decision.
If you don't have livestock, you're in luck. I would slap some sponge filters on the end of the powerheads and rinse them out as the SD silt gets sucked through. That will take care of your immediate problem. Cycling and aging the Sd will make it heavier and it will calm down. Just make sure you go with a deep sand bed right away, because it's tough and time consuming to convert down the line (like I'm doing). Good Luck!