Despite preferring not to comment on Hydro, I think you might have answered the question.
It will be an issue indeed that the reservoir temps will be too high, and therefore very warm water will be feeding the plants continuosly which is not a good thing at all.

A light mover would be the ideal solution but I'll have to save up for one as I am totally broke at the moment sadly. Can't even buy any green!

I guess another option would be to master the soil grow and ditch the hydro altogether, now that I know that hot temps aren't so scary afterall.

Hmmm, no reservoir, no buckets, no ridiculous amounts of water, no pumps, no rockwool... its sounding good already!

Cheers again Rusty.