I am pretty consistent in my tank maintenance, but when I swapped my gravel out for sand, the amount of waste that was under the gravel was amazingly gross. It looked like sewage. I did the change with the fish in, and it worked, but after doing it, I would recommend removing the fish to a bucket with tank water and an air stone, then just change everything at once, it will be less work. Not having all that crap under the gravel is the biggest advantage I have seem so far, and next would be the filter does a great job of picking up all the poo. If you make the change, and you don't yet have a power head, invest in one. Your tank will look so better, and with my Africans, they love it.