Felf, I was given a 55 gal sw
tank with sand. I use it as a FW
tank so switched the cleaned sand out for 30 lbs of Estes gravel. I used a large fishnet and scooped the sand out as best I could, siphoned the rest into a bucket then threw in my rinsed gravel. The fish stayed in. I turned my filter off just in case but the sand did not move around as much as i thought it would, I did not have any floaters (the sand I mean
As far as beneficial effects other than appearance, it would probably close off some pockets of substrate that might gather decaying food. Maybe if you did want to switch to plants, it would give them something better to root in, depending on the sand. I have heard that a 50/50 mix of gravel and fluorite or onyx sand is good for plants but I do not know what kind of sand you are using.