Ant, I'm going to stick my neck on the chopping board once more and say you need to move those tanks out of the conservatory, there is no point having a heater set to say 24C and having a temp way above this all summer long (doing the fish no good at all).
A single tank at a time, syphon tank water from your tank (having turned off the heater and filter) to half fill a "fish only bucket" and net all your fish from the tankinto it.
Then remove all the water from the tank and move the tank to another room, where the tanks will not get blasted with direct sunlight (a north or west facing window room would do nicely).
Add new dechlorinated water to the tank, get the heater and filter going for 10 minutes or so.
Drip acclimitise the fish in the bucket to the fresh tank water before netting back into their moved home.