Again, environmental restrictions may dictate the use of copper-free antifouling bottom paint. Typically, a higher percentage of copper in the paint means it’ll be more effective at combating shell fouling. But copper-free bottom paint containing the eco-friendly biocide Econea (tralopyril) has proven very effective on shell fouling such as acorn barnacles and zebra mussels. If you have an aluminum boat, you have to use a copper-free antifouling paint to avoid galvanic corrosion, which will destroy aluminum. Underwater metals also need bottom paint that’s copper free.