I live in Southern California in a house is 4 years old.  About a year
ago, my hot water recirculation system began springing leaks near the
recirc pump at the water heater.  The 1/2 inch copper piping was
eroded/pitted at the elbows and two separate pinhole leakes developed.
 I tested the water, and there didn't seem to be much unusual about
the it, other than it was hard (25 grains?).  My water also heater
sounded like it was already scaling up.  I replaced the piping and
installed a rotometer and a couple of valves to that I could slow down
the recirculation rate - from what I think was around 7fps to about 1
fps.  I also installed a water softener on the hot water supply about
6 months ago (water now less than 1.5 grains?).  Now I have noticed a
white granular sludge building up in the rotometer and recirc piping. 
The only place I can think it is coming from is the water heater, so
I replaced that.  What is going on here?

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Request for Question Clarification by tox-ga on 14 Jan 2003 17:18 PST

druss-ga,
This may be caused by a certain electrochemical effect.  Could you
check and tell me if at any point near the leaks there are two
different types of metals touching each other?  So what I mean is, are
there any, say, steel pipes touching copper pipes?

-Tox-ga

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Clarification of Question by druss-ga on 14 Jan 2003 20:39 PST

No.  It is an all copper system with brass/bronze fittings - except
for the water heater, of course, which is a glass lined steel tank. 
The fittings on the tank are steel, but they have plastic liners -
althought the liners were pretty crapped out on the old tank.  I
thought electrolysis of some sort might be involved because the
pitting that originally ocurred was unusual-it looked more like
cavitation damage than simple erosion. (I can send you photos if you
wish.) But no one I have shown it too can figure it out (including my
neighbor who is an egineer in the municipal water industry).  I'm
probably more worried about the sludge at this point, since the piping
I replaced shows no signs of wear so far.  I haven't had it tested,
but I assume the sludge is some sort of calcium and/or potassium
carbonate - the hot water outlet at the top of the heater was clean,
but the recirc piping, which feeds back into the tank drain, was full
of it.