"RE: Rock / gravel bottom" 10:34am Monday 22nd Jun
joined: 8th Nov 12
last here: 3:50pm Tuesday 7th Jul
Definitely a bad idea to have gravel as mentioned previously is a breeding ground for bad bacteria and detrimental to fish health. Also impossible to keep clean.
Rocks are just another object for your koi to damage themselves on and also will trap muck and harbour bad bacteria.