I had kept some filter media intact, and it would have only be power off for 30 minutes. The rest of the gravel etc was given a light vac as it was emptied, but not washed in other water. The tank was set up for a couple of days prior to fish going back in, and they had been in there a week when they up and died.
The remaining fish are looking better, I had to get another clownloach today to keep the remaining one happy (wouldn;t want it karking it cause it was lonely).
I will definately take more care now.