Removal of fluoride.

It sounds like you are using the right treatment for the fluorides.  But because many fluorides compounds are slightly soluble, you will have to do what you can to drive the reaction in the favorable direction.  Probably the easiest thing to do is use a gross excess of the cation (calcium, aluminum, etc), which should drive the reaction toward the formation of the insoluble species.  I'm not intimately familiar with the kinetics of the reaction, so I'm unsure how strongly temperature plays a role or how much excess cation you will need.

You may also want to investigate using multiple treatment steps.  In vessel 1, treat as you normally do.  Remove the precipitate and pass the liquid on to the next vessel.  In vessel 2, repeat the treatment.  Depending upon the amount removed at each step, you may need more stages.

This method may require more upfront capital due to the additional reaction vessel, but it should cost less in chemical costs long term. 

Jack:  I did a little research on this and found an article of others having trouble getting the flouride level below 10mg/L.  Go to google and type in: EPA-600/2-80-058

Or click here....

   Hope this helps.

    Jim