Susspeciouse deaths...

Today I got home to find in one of my tanks my new (caught 3 days ago) valantini puffer... Resting... On his side... Dead. I was busting to piss so I only had a quick look on my way past, I came back to remove the puffer only to find 5 blue green cromies and 2 saddle back clowns had also carked it. The only survivors were inverts, 1 juvanel percula clown and one goby.
Everything seems okay test wise, the only thing I can think of is somehow the puffer has died and released its poison into the tank killing the other tank mates, I don't understand why the goby and percula didn't die as well, out of all the tank inhabitants the percula clown would have been under the most stress as the saddle backs didn't like him in there anemone, so I would of thought he would of been the most stressed and therefore most susceptible to die. Previously to this everyone was eating and getting along great as far as I could see.

Any ideas on what has happened guys? Or any ideas on what I should do now? As in how long does the poisen last, will it dissipate itself or do I need to do a partiall or full water change?

Cheers Simon

It was the puffers poison mate and it will not show in any test.
It’s hit and miss as to who is capable of handling the toxins from these fish in a closed system. After a few weeks of tank life, if it happened then, the deaths would most likely not have occurred, they lose the majority of their toxic content after some time because they get most of it from their intake from the wild.
Your bio media will take care of it in time, but a water change would be good.
Do you have extensive external filtration?

They were in a Red Sea Max 130d, so not really, the filtration system is pretty basic in them. Just a bag of bio media, bag of carbon, shitty skimmer and live rock in the tank

That’s pretty much why mate, not much bio filtering to help cope with it and extra water as in an external bio filter that would have reduced the parts per million of the toxins.
What happens when the system does cope and there is enough water to defuse it is most of the time a fish or two will develop what appears like warts, but is a fungal infection from the toxins languishing in the waters for a time?
It does go away!
Activated carbon can work,i tried it once and it didn't work for me,but some say it does work.Personaly for a small tank i would use a chemical reactor.But then that's similar any way,just these days it is probably better carbon,lol.