helphelp - really high water hardness

I have 9 guppies in an 80 litre tank (about 20gallon I think??) just a
corner filter, light, heater, plants and gravel. I bit the bullet and
coughed up $60 for a test kit for all the usuals. Acidity is 7.5, Nitrites
0ppm, Ammonia .25. What is really stressing me is that my waters hardness
is off the scale (the test kit reckons if you add 11-22 drops of reagent to
the sample, this goodfor rift cichlids I gave up counting at 30! )
My tap water is about 9 drops, but obviously the minerals have built up.
I have just done a 50% water change (I know adding MORE minerals) but my
problem is that I wont be able to buy water softeners for another week.
Is there any way I can bring down the hardness with stuff I may have around
the house?

Any advice much appreciated.
Cheers
Lilly