Thanks for the reply.
Is lack of oxygen the biggest problem (as opposed to heat stress on the
pump) at high temps? If so then could an airpump be a solution here (even if I'm trying to minimise electrical components)?
I read in another thread someone puts frozen bottles of water in the reservoir in the morning on predicted hot days to keep temps down but it's a pretty primitive solution with varying results (depending on temps).
There are probably big gaps in my knowledge so I appreciate the patience
