Nemrod, I didn't imply that you or captain stirred up silt. I was simply reacting to your statement that, since someone wasn't in a cave or a drysuit, they didn't have to worry about fanning a silty floor. I think they do. I would hope that neither of you would turn head up and fins down and kick when only a few inches above silt. I suspect you wouldn't.
Simple physics says that aiming your fins at the sea floor is going to push water there, and water hitting the sea floor will disturb whatever sediments are present. If it's rock or coarse sand, it won't do much. If it's fine silt, it will. Whether you're DIR or anything else, you need to avoid kicking water into fine sediments, if you want to preserve the visibility where you are.
Simple physics says that aiming your fins at the sea floor is going to push water there, and water hitting the sea floor will disturb whatever sediments are present. If it's rock or coarse sand, it won't do much. If it's fine silt, it will. Whether you're DIR or anything else, you need to avoid kicking water into fine sediments, if you want to preserve the visibility where you are.