If you have a buddy at a local dive shop that you feel will give you truthfull advice, they will tell you what they use to strip the old paint also this should be done only prior to your hydro only, is what i was told buy a professional at that taught my gas blender class. I have also learned never buy a painted or laquered finish tank if you dive salt water. Shot blast or unfinished brushed finish. My one unfinished brushed finish tank looks better than all the rest. Every year before VIP I peel all the stckers off and toss it on the roller machine with only a non abrasive scotch sponge (you know the dish sponge with the green pot cleaner on one side) with a soapy water solution(2 able spoons of dish soap to a quart of water. In less then 3 min. it looks like new, if you don’t have acsess to a tank roller. A 25-30 min hand rubbing will also work. What ever you do don’t be tempted to use any thing more abrasive. This also looks good on painted tanks that have been stripped, but dont ever expect a stripped tank to look all pretty and shinny, it just cant be done. If you do strip your tanks please do not paint them, use those shrink wrap skins if you want to be fancy. Another person I know, waxes their stripped tanks and then puts those skins on them. They have been holding up about 2-3 years. Good luck with what ever you do.