I'm getting a build up of a clear jelly like substance in my feed and expansion tank for the central heating. It's a new system with all the correct system cleaners and inhibitors in. I've emptied the tank washed it out and refilled it and added a fresh dose of fernox, but still after about 6-8 weeks the build up is back. The worst part is it sticks to the float in the tanks and causes it to sink, and overflow, so i can't really trust it and have to keep checking it every week. Any ideas on whats causing it and how to prevent it ??