so you think the main problem is his water temps?The non-healthy root systems in the photos tell a completely different story. Temp is definitely affecting the grow.
light is the cause
temps might be a part of the problem, but black out that root zone with a little h202 in the mix and im sure he will be good to go
not a fan of moving a frozen bottle in and out of your tank, but maybe i like to take a cleaner approach
/everytime you open your reservoir you run the risk of contaminating your solution