Twinkle is turning yellow

[hera]

I bought an Onc Twinkle in March and it is still growing new bulbs, but the ends of the leaves are turning yellow. No other signs of rot, I unpotted it and the roots are the usual some dead and needing trimmed and some alive and growning. The plant looks good except for the yellowing leaf tips. I have heard mixed advice on growing Twinkle. Do you think that it is fertilizer burn? How sensitive are they to tap water? I could use some culture advice from some of your success stories. I'm not sure what to repot it in( fine bark, sphag, etc) I thought about s/h but one other post hear warned against it.

[brookn]

I have two Onc. ornithorynchum, and I do not fertilize, except for worm poo. The last time I used fert. I got a couple of brown leaf tips, so I stopped, but I am not real big on fert. anyway. I have found them to be very hardy, and I use tap water on it.