I have a coloured gravel substrate in both of my tanks.
Three main reasons I am switching to a sand substrate:
1. I have Schwartzs cory (Corydoras schwartzi). Sand will make them more comfortable.
2. I have 2 amazon swords, a wide leaf sag (Chilensis), and two something that look like ludwigia repens. Only the swords have rooted kind of OK. Others will be easier in the sand.
3. Education! I want to gain some experience with different substrates before I start my 120g.
The journal entry starts with finalizing what I am going to use, and pool filter sand or play sand (whichever I find first before going to home depot) is the winner!