Pond types seldom get buoyancy issues but if they have not been eating floating foods or foods with too much starch, then this is down to genetics and is seldom fixed.Possibly, he seems to be able to dart up and kinda bop around side to side but he always goes back to the bottom...
If that's it, is it fixable?
Watched the inches for a while... the one with the blood in his tail was being picked on... I probably made a bad choice by putting him inthe small part of the pond because of risk of infection, but I really had no other choice. he would have eaten the newborns and probably have picked on the smaller ones. I just hope the inches don't start picking on someone else.