why are my roots burning?

i have cloned bluberry. they are 3 weeks old in promix at 6.5 ph under a 1000watt metal halid, temp is at 80 degrees.

ever since i started feeding them nutes they have been burnt.(indicated by the tips of leaves turning brown after feeding). im using botanicare products. they are three weeks old and im only at 10 mill of veg nutes per 5 gallons. any more than that and they burn.

at 3 weeks old with other strains im usually at 30-35 mill of veg nutes per 5 gallons.
is blueberry a light feeder like that or are more roots sick?

I have heard that blueberry is a tricky strain to grow for this very reason, hopefully someone with real advice will respond. You should describe the reasons you suspect root problems.