Dark spot

[Paladin]

I bought my Catalina AL80 new in 1991. Not long after I bought it, I got a bit curious and drained the tank completely. I then removed the valve and dropped a light into the tank for a looksee. The tank looked clean and new except for a small dark spot in the very bottom of the tank. The spot was about the size of the fingernail on my little finger.

I took it back to the shop and asked the owner about it. He told me that it was just a harmless discoloration in the metal and not to worry about it. I used the tank regularly for five years, had it VIP'd every year, then stored it away with 500 psi in it.

This past spring, I decided to get back into diving and took the AL80 and my old Healthways steel 72 to hydroed. Both tanks passed hydro and, later, VIP. The shop where I took them made no mention of the dark spot in the AL80. The spot is still the same size that it was in 1991. Anybody know what it might be? It kinda bothers me, but not anyone who has ever inspected it.

 

[DA Aquamaster]

It is indeed a harmless dark spot. At some point there was most likely a drop of water there. it is not uncommon to see the same discoloration over a larger area of an AL tank and to see numerous small spots. In some cases you can actually see streaks where droplets have obviously ran down the tank.

Whiteish colored powdery deposits on the other hand would be a concern as they indicate an active oxidation process.