White Snoop is so right on about keeping the res temp below 70. Also added air to your res can really help. Hydroguard added regulaly can help. Also with the roots in bad shape Super Thrive and Advanced Piranah instead of nutes can help. The H2o2 kills the fungus and works like a cannazym to wash away dead roots. Then a regiment of the Super Thrive and Advanced Piranah or GH Subculture adds friendly bacteria to help rebuild a root structure.
Good Luck