F8s are mostly found in FW rivers in the wild, making frequent trips into BW estuaries. After a decade-long study though, it has been determined that in captivity, they live longest in low-end BW--SG of around 1.005--up to 18+ years!
Some species of puffers need a daily supply of crunchy foods. Others are good with 2-3 feedings of hard-shelled foods/week. I usually mix it up with softer foods, like worms & harder foods like shrimp, every other feeding. I do not feed my puffers every day though. Once their teeth are overgrown however, there is no amount of crunchy foods that will wear them down. At that point, they must be hand-trimmed by their keeper.