The issue with bottom paint
over aluminum is that most bottom paints contain copper. Copper reacts with the aluminum (creates a battery) and therefore you need an extensive primer barrier system (6-8 coats of high build epoxy and 2 coats of a strontium chromate primer (for a total of at least 25mils). Quite extensive, quite expensive.
Therefore, the solution by bottom paint
manufacturers is to offer copper-free bottom paint. i.e Trilux. However, they do not perform as well as traditional copper based bottom paint. You dont have to worry about them reacting to the aluminum, but they just dont perform well.
The best solution I have seen out there is Smart Solution by Sea Hawk Paints
. I have heard of great results compared to the other copper free bottom paints! Much better performance than Trilux. However, you do have to clean the boat because it does get soft growth (slime)...but no hard growth. I know you can put it over your existing bottom paint. They dont claim 6 years...just the normal year or 2 like all bottom paint.