Chara is probably my LEAST "favorite" aquatic pest to challenge. Its presence indicates that you have very hard water (so I'd rule out the use of copper sulfate - period). A chelated copper (eg CUTRINE PLUS GRANULES) may be useful in knocking the chara-population back for a short period. However, if you continue to have ultra-clear water (my bet is that your water is crystal clear - ???), the chara will very likely return in fairly quick fashion. So, I'd also suggest implementing a plankton-inducing fertilization program (to reduce sunlight penetration) following the chelated-copper treatment. The sooner your water clarity is reduced, the less problem chara will present in the deeper areas of your pond.

Kelly Duffie
Cypress, TX