Anode / Antifoul Interaction

[Psalm8]

Hi Folks, need some help please. Hoping someone has experienced and solved this problem. I have a 5yo 12 metre GRP yacht now on slip for third time.
Had significant growth around refrigeration heat exchanger (part of gallery outlet) approx 200mm diameter. Same around large hull anode approx 500mm diameter. I'm using Altex copper based antifoul.
At the previous haul out had similar thing at refrig outlet which I figured was the localised warmer water - probably wrong.
Now not sure whether it is a reaction between antifoul and anode or too much anode material. Anodes are as supplied sizes on boat except hull item (about 25% larger) was replaced 17 mths ago.
Anyone seen this?
cheers
Sorry, failed to mention when we water blasted the growth off all the antifoul was gone?we wen
Psalm8

[perchance]

Dissimilar metals = galvanic couple = loss of metal from the less noble metal or something to that effect. On power boats the anti foul is to be kept a minimum of two inches away from the aluminium transom mount.

[Psalm8]

Yes I was thinking something like that and therefore of using the antifoul a less copper rich antifoul around the anodes (ie the antifoul I use on the saildrive leg)