[Arabidopsis] growth problem: terminal cotyledon stage?

[Dan Riggs]

Dear All:

We have a plant growth problem that is somewhat baffling and I'm writing 
to ask if you have some advice or experience that you can share.  
Seedlings germinate nicely on Premier Pro-mix PGX (which we have always 
used), but remain at the cotyledon stage for weeks; they then either die 
(about 90%), make flowers when 1cm tall, or 'come out of it' and produce 
nice, normal plants.  There's no correlation with genotype: a variety of 
mutants as well as several 'wildtype' ecotypes exhibit this.  I suspect 
the potting medium and have a different type of soil, but the jury's 
still out on that aspect.  Could water source be a problem (ie, rusty 
pipes)?  Have any of you any experience with watering with distilled 
water.   Thanks for your time.

Dan