I think you have it reverse. Hard water doesn't affect AS- AS affects hard water.Hey I was just wondering how hard the water would be to really affect the soil? I read on site that harder water would affect it. I wanted to try using it in my 10 gallon since I found it in my LFS for $26, same price on the site.
With its price being close or cheaper than flourite or Eco- you should give it a try.