Mass larvae deaths

I got a number of Lisso Montandoni eggs from here on the forum which hatched 2-3 weeks ago. Of the 22 eggs there was one dud and three early deaths, which I didnt think was bad.
They were originaly kept in a plastic aquarium with an airstone but cleaning it was really awkward so about a week and half ago I switched them into a pair of shallow 5 litre tuppaware containers(without airstones). I'd been doing 90% water changes daily with tap water(aged 2 or 3 days). They were feeding happily on live tubifex.
As I was going out straight from work last night I changed the water at lunchtime, got home a few hours ago and 17 of the 18 were dead.

I'll admit having only raised newts from eggs a few times in the past I dont have a great deal of experience but I've never had this many go to the big pond in the sky all at once overnight - does anyone have any suggestions what might of happened? Did I do something wrong?

I'd been really enjoying them too

I dont have many answers, as I've only raised larvae once, but did the temperature spike at all?

I'd expect it dropped overnight, but it wasnt an overly cool evening(I slept outside). Couldnt have been more than a couple of degrees.

Sorry to hear about your wipeout. Environmental causes are the most likely, perhaps the lunch time water change was contaminated? An other option would be a bacterial infection but I don't know how likely this would be. I would expect slower death rates from an infection; you'd see sick larvae rather than all dead larvae. Contaminated food perhaps?

Move the survivor to a fresh tub.

I dont think contaminated food is likely, other things fed on the same tubifex seem to be fine.

Water may be a possibility, thinking about it the buildings water had been turned off for 8 hours the day I filled those buckets for repairs(a weekly occurence in this dump). I always run the water for a couple of minutes before I fill up, something in the pipes perhaps?

Maybe. Things can build up in the pipes as I'm sure you know. I don't know how sensitive larvae are, if just a change in water composition like that would kill them, whether the new water was necessarily bad or not. Maybe next time you can try raising some with the "pond water" method and see if that works better (what I mean is, regular fish tank water with just an air bubbler and no water changes).

I feel really bad for you!

With the amount of waste and live foods needing to be in there I would have thought water changes would always be nescasery, trouble is with only one fish tank I'm not sure I'd have enough water to manage it as often as I'd need too..
Hopefully the one left will survive, might just stick to buying morphed juvies in future :-\