Aluminum Water Tank for leak testing - best material and water solution???

We currently use an aluminum water tank for leak testing gas tanks under an air pressure of 1.5 to 2 psi.
The water tanks are severely corroded above the water line and I do not know what aluminum alloy was used but it was most likely either a 5052 or 3003 sheet in the annealed -O temper.
I am assuming the corrosion was accelerated by the fact that we used chlorine bleach as a disinfectant to keep any micro-organisms from breeding in the water.
Does anyone have any good ideas on the best aluminum alloys and water solution disinfectants to use such that corrosion of the aluminum tank walls is minimized?
We are probably going to weld up a new water tank soon.
Thanks in advance.
Giorlando

Iodine does a good job of preventing any funk from growing in the water.
Hikers use it to sanitize lake and river water for drinking.
-Tom
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Plastic coating