FW coled (heat exchanger) no anodes to my knowledge. In my desperation to prolong life of heat exchanger (aluminium casing and copper tubing) I do use this product:
Injection into raw water stream ("nip" to 1l of H2O mixture) is done by 100ml/min 12V chemical grade displacement pump, inter-conected to suction side of raw water pump (check v/v and isolating ball v/v in line):
To early to coment on benefits of this procedure or product. To describe nature of this chemical: it takes several pieces of paper towels to wipe it off, but remaining smuges need some more. Lets hope it is equaly resistant to raw water wash. 
