Harry,
You have a few different options when it comes to higher temps with the reservoirs.
-Chiller (end all solutions but expensive/use a good amount of electricity/output heat)
-Beneficial Tea
https://www.rollitup.org/dwc-bubbleponics/361430-dwc-root-slime-cure-aka.html great cheap solution and super easy to use, would def recommend.
-Sterilization (frequent h2o2, dutch master zone, or similar cloramine (ewww) based products) can keep roots looking super white and clean looking but harsh products.
I've used several chillers and after having a second one die on me I'm really fed up with replacing these expensive but cheaply made units. The tea has some stellar results
and in addition to keeping roots healthy, you're also creating a symbiotic relationship where the roots will feed the beneficials and the beneficials will put off an enzyme. These
enzymes will help to break down food for the plants even faster helping to enhance that hydro speed even more. The thread I linked is pretty long but just crammed packed with
useful information for hydro peoples