Been messing around with fillers on my 510. I thought I had settled on Fluval. It worked great for a few months, but I developed asthma-like symptoms. I switched from PG to VG, to no avail. I finally switched back to PTB filler, and all symtoms disappeared, almost overnight. There was no evidence of it, but I guess I was smoking foam. My personal experience indicates that PTB is still the best filler for 510 carts. Your milage may vary.