Thanks guys. I was having such a good year up until now - four clutches hatched successfully so far and a great year for non-feeders (i.e. very few).
I guess it's only fair that Murphy should have a go, but it's heartbreaking to see them get this far and then not make it.
Why exactly are you using an aquarium thermometer (a not so good one at that)? Investing in a good digital thermometer would be wise so that in the future you know if it's a heat spike that caused the problem.
While it sucks, be glad it's a clutch of amels and snows and not a clutch of hypo stripe lav bloods or something. Last year sucked bad enough, but cracking open a container of dead snakes consisting of 3 hypo sunkisseds and a handful of sunkisseds sure sucked a big one.
As I said in my original post, I check the temps regularly with an infra-red thermometer. I also used that to set up. The old aquarium thing is in there just as a quick indicator of potential trouble when I first open the lid - I don't rely on it.
But that won't help you at all to determine if their was or wasn't a temperature spike when you weren't their measuring the temperatures. They make digital thermometers that track that information (and they're pretty cheap too).