Calcium in nickel plating solutions can frequently cause difficulties particularly from the
standpoint of roughness and, more recently, by plugging up the holes in air-agitated
systems. The needle-like crystals of calcium are familiar to many people and
identification is simple. However, plugging of air pipes can be the result of materials
other than calcium deposits, for example, boric acid, and identification of the material
should be made before arbitrarily treating for calcium.

An effective method to reduce the calcium concentration to tolerable limits is by taking
advantage of the decreased solubility of calcium at higher temperatures. To accomplish
the reduction of calcium concentration, the solution is pumped to the storage tank and
then heated to 160-170 F and this temperature maintained throughout the procedure.
After allowing several hours for the precipitation to take place, the solution is filtered
back to the plating tank. The filter must then be cleaned before being returned to the
normal task of filtration; if not, it is possible for some of the calcium to re-dissolve from
the cake when the temperature should be taken into consideration before performing
this treatment.

Another method, which is somewhat more complicated but more effective, is the use of
sodium biflouride to precipitate insoluble calcium fluoride. Because of the fact that
excesses of fluoride will reduce the leveling of the deposit, it is first necessary to
analyze the solution for the calcium content. Since magnesium will also be precipitated
and can be present in substantial amounts, this must also be analyzed. The procedure
is as follows: