Originally Posted by AbbeysDad
Hey Nick, welcome to TFK.
Lots of folks here have replaced substrates successfully. There are a couple of things you can do to minimize any beneficial bacteria upset. Since (I think) you don't currently have plants, you might add some floating plants that will help deal with ammonia as things settle out. You could also bag some of your existing gravel in media bags or nylon stocking material and leave in the tank for a week or two following the change. Since you're filter remains unchanged, a fair amount of biology remains there so with other measures, the transition should be smooth.
Note: I'm probably overstating the obvious, but be sure and rinse the new sand really well as lots of folks have issues with cloudy water following the change to sand as very fine, dust like sand particles can be a real pain.
I would also leave a fair amount of mulm in the bottom of the tank when I removed the old substrate.
This will help accelerate bacterial activity in new substrate, which might also prove beneficial to plant's by helping to breakdown organic's a bit quicker which would feed plant's.
Would toss a few trumpet snails in the tank as well to help sift,aerate the sand.
Only saying this is what I would do.