Since, finding red garnet sand is impossible. I just transitioned to the same type of red gravel such as yourself. Although it's stunning look to the fish. But .... I overlooked the thought of the poly ingesting during feedings. I didn't really think about the risk. What are your thoughts or those who is reading this post?
I just witnessed my 18" ansorgii regurgitate some gravel out. It's a weird sight to see. They do a slight V motion 4-6 times between the head and arched back. It happens when certain ones overeat and gut load themselves. I'm sure all of you seen it before with large polys.
Honest opinion I don't feel as tho gravel is that harmful... Don't get me wrong! They can swallow it and it can kill them! But in all the time iv ever had gravel iv only had 1 injest a stone that I no of and it passed without harming the bichir .... Iv seen them get rocks in there mouth but they usually spit them back out from my observations