My guess is that the lighting intensity changed for this rock and the algae
color is changing due to it. This will happen in corals many times when the
algae inside must increase or reduce due to light intensity.

In my tank the light that is directly hit by the MH's is a lighter purple
than that which is in a shadow.

Probably not what you wanted to hear....you could try to put more actinic,
but it may not give you what you want.

LT


"RLIrwin" wrote in message
...
I'm very new to sal****er aquariums and I need some help. I have a 10
gallon
aquarium with two clownfish, a couple of hermit crabs and a four astrea
snails.
I have flourescent light that I leave on 10-12 hours per day. I have a
filter
that hangs on the back of the tank (millenium 1000) and an under gravel
filter
- so I think that water movement is pretty good. The water chemistry is
as
follows: ph-8.2-8.4, ammonia 0, nitite-0, nitrate - 5 - SG-1.022, Alk -
normal, Ca - 450, dKh - 11. Temperature is kept at 78-80. I also have
begun
adding the kent trace elements product. I change approximately 2 gallons
every
other week - beginning with RO water. About 4 weeks ago I got some fiji
live
rock with reasonably good coverage of purple coralline algae, some
sponges, and
a few pollyps of some sort (white translucent). Everything seems to be
doing
ok except that the coralline algae is fading in places to a white color
with
just little green. I'd rather keep in purple if possible. Any
suggestions?