Thanks for Reply Ron. After posting thread I did some more research and located several articles concerning concrete and aluminum. Aluminum is a common type of concrete form material. Apparentlty there can be a reaction between the unoxidized aluminum and the calcium hydroxide released during cement hydration. The reaction produces hydrogen gas. I was concerned about an old aluminum tank to be used for final curing. After further research I am no longer concerned the old aluminum tank will adversely effect the final curing of the concrete cylinders. You may already be familiar with this but I found it interesting that lightweight concrete can be produced by adding aluminum powder to the mix.
Thanks again