Hey Duggy i'm watching closely as i've just picked up an EC meter for the next run! (so im watching yours!! ^_^)
I was scouring the canna website the otherday and reading what they say about rhizo (i've always just dumped a couple of ml into the mix) - Do you foliar feed with it?
They recommend foliar feeding with it at 4ml per litre on the site and thought that may be a bit heavy for a seedling? - What's your thoughts mate?
I noticed that too. So, I have been spraying a touch of cal/mag + Rhizo. No burn so far. Believe I added around 2.5 ml to a quart size spray bottle with RO.
Started seedlings at a week and 1/2. Rhizo is for any plant with roots. Couple of weeks or so should be safe because they grow roots so fast.