[RichH]

If you have access to a ''technical water'' company .... one who specializes in Reverse Osmosis or Ultrafiltration Membranes ---- "US Filter", Minntech, or similar local firms, see if they wont sell you some "Peracetic Acid". Peracetic Acid diluted to a 1% concentration will kill just about everything inside your tankage within a few hours --- but wont dissolve all the debris so you''ll have to periodically add some ''disinfectant'' to retard new critters from eating all the ''old dead bodies'' that remain. Peracetic wont be aggressive vs. aluminum as would Chlorinated mixes.
1/2 gal. of peracetic diluted per 50 gallons of tank water should do the trick .... and with minimal ''damage'' to the aluminum but any acid will dissolve ''some'' of the aluminum. The solution can be dumped directlly overboard when done soaking .... or simply dump a few boxes of bicarbonate of soda into the bilge, etc. and mix there to neutralize before discharging. Obviously you will have to thoroughly and repeatedly rinse the tank until all is totally diluted out.
Obviously the usual ''chemical safety warnings'' apply: heavy rubber gloves, chemical goggles, vinyl apron, knowledge, etc.