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Inhibitory effects of Manganese?

I am wondering if this has been discussed before, but
I was not able to find anything on a search of the archives.
I'm also not sure if this information is outdated, since I
read it in Wetzel's 1975 edition of Limnology.

Anyway, the passage that interested me was as follows:
"High concentrations of manganese (>1mg/l) commonly are
very inhibitory to blue-green and green algae (Gerloff and
Skoog, 1957; Patrick, et al., 1969).  An antagonistic response
was demonstrated in which increasing calcium concentrations
progressively reduced the inhibitory effects of high manganese.
<snip> Manganese concentrations of <50ug/l were found to
inhibit the development of green and blue-green algae in streams
and to favor diatom growth strongly."

I am wondering if an increase in the [Mn] (or even just the fact that
it is already in the PMDD mix) would give an additional algae fighting
attribute to the use of PMDD?  I realize that Mn can be toxic at higher
levels, but am unsure what those levels would be.  As mentioned it would
seem to favour diatom growth, but hey, our otos would be happier anyway.

The two articles cited are:

Gerloff, G.C., and F. Skoog.  1957.  Availability of iron and manganese
    in southern Wisconsin lakes for the growth of Mircrocystis aeruginosa.
    Ecology, 38:  551-556.
Patrick, R., B. Crum, and J. Coles.  1969.  Temperature and manganese
    as determining factors in the presence of diatom or blue-green algal flora
    in streams.  Proc. Nat. Acad. Sci., 64: 472-478.