Aluminum scuba tanks are great. They are cheap and lightweight. The only problem is their buoyancy at the end of the dive. They tend to invert, and this makes it necessary to add some sort of trim weight.
I used to just strap a 3lb weight above the tank boot with a conventional weight belt. It had a tendency to rotate around. When it rotates around to the front, it can hit you, and it’s just not comfortable. There had to be a better way.
I had an old wetsuit from 1996, so I thought I could cut it up and make a nice tubular weight. I couldn’t get my machine to sew it without binding so I had to do it all by hand. It locks on with a Velcro sandwich and evenly distributes -3lbs evenly around the bottom of the tank. The lead inside is #4 shot and it’s actually a little more than 3 lbs to offset the positive buoyancy from the neoprene.