HELP! Staghorn Algae! Water Softeners, and other nutrient questions

[Cheryl Trine <ctrine at andrews_edu>]

Hi all,

I've been following this list for a couple of months now, and have
really learned a lot just lurking.

I am having trouble with poor growth of some plants and luxurient
growth  of staghorn algae.  Tank parameters:
10 gal. with two 13W screw-in CF lights
Set up in January 2003
Substrate: Fluorite (replaced gravel 2 months ago)
Fertilizer: Seachem Flourish--once a week, amount according to the
directions on the bottle
pH: 8.2
GH: 1 degree
KH: 15 degrees
Ammonia: 0 ppm
Nitrite: 0 ppm
Nitrate: < 5 ppm
Fish: 2 black mollies, 2 panda cories, 4 guppies
Plants: Water wisteria and some other form of Hygrophilia, Rotala, Java
Fern, Vallisneria

The wisteria has grown well and does not have a lot of "aerial" roots;
the Rotala, has for the most part just sat there, there is some new
growth, but the leaves are very small and internodes very short, Java
Fern is producing new plantlets; Vallisneria is just sitting there.

I have quite hard water (18 deg. GH, 15 deg. KH) coming from the city
water supply, with a pH of 8.2 - 8.4.  I'm using a household water
softener with the potassium salt rather than the sodium salt for the ion
exchange. Is this softened water O.K. to use with the plants.  It should
be providing K, but would it provide too much?  Is it likely to cause
some other nutrient-related problem?  Am I creating other problems by
removing the Ca and Mg?  Should I mix city and softened water?  I'd
really like to know what to do to get rid of the staghorn algae and get
better plant growth.

Oh, one more thing--I used a yeast-soda bottle source for CO2 for
awhile, but quit when the staghorn algae started getting out of control
about a month ago.  Should I start it again?  Should I go without CO2 or
fertilizer?  I'm really at a loss, this is so new to me!

I appreciate any advice!

Cheri