As noted above 2-4 pounds is probably all you'll need at most with a pair of AL 80s after it's all said and done with the swing weight, regs, tank rigging, residual gas, etc if you are pretty much neutral in the water with no tanks on at all.
Thee are two schools of thought with AL 80s.
One is to add any needed weight to the tank to normalize the tank relative to other steel tanks you might use that end the dive near neutral or a couple pounds negative. In this case adding the weight to a cam band near the bottom of the tank also helps offset the tail light trim of AL 80s when they get low on gas. And that also tends to be the simple solution as the lower clip is often secure with a cam band when you bring your own rigging to put on rental AL 80s.
The second is to attach any needed weight to a weight belt or to your harness in some manner. I think this approach makes the most sense in terms of divers who do not need ay weight at all, something that is not uncommon in fresh water, in a 3mm or well crushed from use 5mm wet suit when the diver is carrying reels, back up lights and a can light, and is diving in a manner that leaves a 1/3rd reserve (1000 psi) in each tank at the end of the dive. In that case in particular, it makes a lot more sense to carry no weight on the tank and just clip them to a waist D-ring when the tails start to float to avoid any over weighting.
Both approaches work fine, but in both cases whether it makes sense or not for you depends on the entire picture of what you are diving and how you configure for it.
Thee are two schools of thought with AL 80s.
One is to add any needed weight to the tank to normalize the tank relative to other steel tanks you might use that end the dive near neutral or a couple pounds negative. In this case adding the weight to a cam band near the bottom of the tank also helps offset the tail light trim of AL 80s when they get low on gas. And that also tends to be the simple solution as the lower clip is often secure with a cam band when you bring your own rigging to put on rental AL 80s.
The second is to attach any needed weight to a weight belt or to your harness in some manner. I think this approach makes the most sense in terms of divers who do not need ay weight at all, something that is not uncommon in fresh water, in a 3mm or well crushed from use 5mm wet suit when the diver is carrying reels, back up lights and a can light, and is diving in a manner that leaves a 1/3rd reserve (1000 psi) in each tank at the end of the dive. In that case in particular, it makes a lot more sense to carry no weight on the tank and just clip them to a waist D-ring when the tails start to float to avoid any over weighting.
Both approaches work fine, but in both cases whether it makes sense or not for you depends on the entire picture of what you are diving and how you configure for it.