destroyed vacation and tank

[WarDog]

+1 to Concepts. This is truly Canada's premier LFS. Props to them for going above and beyond. Happy to hear the livestock is out!

I'm sure your in-laws weren't deliberately trying to sabotage your tank. It takes a seriously anti-social person to do that.
My guess is that they thought they would surprise you with clean carpets and didn't realise the tank water can absorb chemicals as Pike suggested.
Perhaps they used the cleaning bucket to fill the sump/ato without rinsing it (like rinsing would do any good)?
Some people just don't understand how sensitive and fragile our little ecosystems are!
Hopefully the damage is minimal. Looking forward to an update when you get home.