I have not yet bred them. But they are in the process of laying eggs. I am expecting eggs sometime in the next few hours. I do have sand and I recommend it. (Sorry!) but I assume gravel will work too. The reason I recommend sand in because the love digging holes and playing in it! And I read on many online sources that if you have gravel that the fry can fall down into them and get stuck and eventually die. What do u have to breed them in? I use a 6" flower pot that I cut in half(what a hassle that was!!) and they are in that as we speak digging a hole and depositing the sand outside of the entrance. I have 4 different size terra cotta pots of all different sizes. And they chose the smallest one. Back to the sand...it is very cheep if you buy pool filter sand. I got my white sand for $8 for 50 lbs. the only downside is that you will definitely have to rinse it (and rinse it again. And again. And a few more times. And when your done rinsing it, do it twice more) that is because you don't want al, of the particles floating suspended in your water. Good luck breeding the kribs!