I had the same prob with 2 plants I kept in a bag with virtually no light for 2 days. I think it must have been heat or something as they were in the trunk of a car.

Regarding soil mixes my favorite is

60% Sunshine mix all purpose (similar to promix but doesnt get waterlogged like promix...I tried both side by side)
10% perlite
30% composted manure

I didnt have access to it but next time I plan on adding worm castings to the mix.

50% Sunshine mix
10% perlite
20% Wormacastings
20% composted manure

I think this would make a great mix. The plants in my log as curently growing in the a mixture of natural soil and the first mix I mentioned.

JMO Happy Growing