I have a sacrificial anode in my system. It becomes crusty by the end of each season, so at startup I grind off the outside cake before reinstalling it. Whatever the cake is, I would rather have it on my anode than inside my equipment.
That is probably not a good sign. It is very likely your anode is becoming heavily polarized and the zinc (assuming it's zinc, you did not say) is simply oxidizing. Once that happens, the anode effectively stops working.
All ground-based sacrificial anodes need to be bagged and filled with a conductive backfill composition that reduces anode polarization effects. Polarization of a sacrificial anode leads to voltage "hotspots" on the anode surface (uneven electric field distribution) which in turn leads to high current areas, typically around defects and crevices. The over-potential leads to formation of excess scale (typically oxides and hydroxides) which effectively "poisons" the anode surface and stops it form working.
Normally, zinc and magnesium anodes are bagged in a porous cotton sack and filled with a mixture of gypsum (calcium sulfate), bentonite clay and sodium sulfate. The gypsum creates a uniform, conductive medium so that the anode can conduct sufficient amounts of current when placed in soil (soils are typically too high in resistance for the anode to be in direct contact with). The bentonite clay acts as a moisture absorbing material to keep the anode bag conductive and moist. The sodium sulfate ensures that the anode stays depolarized and forms sulfate salts with zinc or magnesium that are easily dissolved into the surrounding soil. As well, proper sacrificial anode design requires that the anode be in close proximity to the structure it is protecting to reduce path length resistance on the connecting wire. As well, the anode area must be matched properly to the cathode area (typically 1:1 or greater) so that the anode does not become heavily polarized.
This is why I commented that attaching an anode to the bond wire probably does very little good. The anode will, in most circumstances, be too far away from the structure it is protecting and it will be undersized in area relative to the the area of the cathode (the object being protected). In most circumstances, when a large object like a pipeline or a tank is being catholically protected, one installs multiple sacrificial anodes at prescribed distances along the object to ensure proper protection.
There's certainly nothing wrong with hanging an anode on your bonding line, I just wouldn't expect it to do much...
