The question is, are these effects common? I assume it's nothing to
worry about, but it's interesting and obvious enough that you've all
probably seen it. What say?

Souds like low nitrates to me and or low phosphate. Iron is probably
low too.

--
Need Mercedes parts ? - http://parts.mbz.org
http://www.mbz.org | Mercedes Mailing lists: http://lists.mbz.org
633CSi 250SE/C 300SD | Killies, killi.net, Crypts, aquaria.net
1970 280SE, 72 280SE | Old wris****ches http://watches.list.mbz.org