Climby, I use aquarium water. I grow in soil under fluros and CFLs. My plants do just fine on it. I'm just an old hippie chick and love my pot. What kind of fish do you have? I have a huge old Jack Dempsey that keeps my plants well fertilized (he killed everything else in the tank except the armored plecostomus). I was just wondering since a lot of fish have problems in hard water.