"Decrease conductivity" of water. How to?

[knifegill]

If my water is already soft beyond soft, how do I further decrease conductivity to trigger spawning in my hoplosternum littorale? Some scientific stubs I ran across online suggest that the only thing that triggers hoplos is this conductivity decrease. Would I have to take it brackish first to increase conductivity, then do a big change to fresh thereby decreasing the relative amount of conductivity? And is conductivity mainly the salt, or all the minerals, etc. that contribute to potential to transmit current?

Or could I just add charcoal?

 

[Zander_The_RBP]

conductivity is just another way to say hardness as all those minerals (calcium, sodium, etc) that cause GH also happen to be metals that conduct. to get it as low as possible your going to have to use R/O water or some other type of water that has 0 GH

 

[knifegill]

My tap has GH of about 9.0. That number is from the state water report, my actual hardness test comes out to 0. That's pretty dang low already, and I doubt I'll ever see a R.O. machine cheap enough. So, unless contraindicated, I think I'll add some lace rock and extra coral, perhaps a bit of marine salt, wait a week, then drop it. Seem like a good plan?