% solids or S.G. meter?

I was wondering which would be more effective in controlling the amount of lime mud slurry to the lime mud fliter, an optical suspended solids meter or a Specific Gravity meter where a correlation is calculated to determine % solids? We use a S.G. meter an a correlation right now, I was wondering if anyone else has any experience with anything else? I'm new to the industry so please pardon any ignorance on my part.