new root tips die when they touch LECA

[razka3]

So I bought this Lc. few months back... and most of the roots were rotten. So I figured why not raise it using S/H culture. So I stuck it in some LECA and watered as usual, did everything correct (I assume). So I start seeing 5 new roots coming out a few weeks ago! Thought to myself that's great... they will take right to the LECA and the s/h environment and will grow like crazy.

Instead to my amazement, during the last few days when the roots came into contact with the LECA the green root tips turned black and stopped growing. The new roots now look awful.

The weird thing is that this is also happening with two other small plants I have put in s/h culture... the new root tips instantly die when they hit the LECA.

And yes, I did soak and flush it prior to using. Am I doing something wrong here? Maybe I should just grow this in bark mix?