Hey Pezzer,
I'm a new grower myself setting up my first RDWC too and was wondering the same thing, so I'm not sure what my advice is worth.
If your room temperature is 30°C, your reservoir might be at a slightly lower temp from evaporation and loss of energy, but not more than 1°C I guess.
From what I've read, dissolved oxygen levels will be impacted by your temperature, as they can reduce by 20-40% when increasing from 23°C to 30°C. So (from what I've read once again), advised temps are 20-23°C.
Furthermore, I believe root rot starts being a serious threat above 25°C..
Hope I was able to help !
Cheers