Mass Death

Question
Hello Jennifer,
We have had a tramatic disaster in our 38 gallon saltwater tank.  I am away for a year, so my mother has been caring for our family tank.  She cleaned the tank 2 weeks ago and then this week she cleaned again.  As usual she did some python work on spots in the gravel which is what I have been doing with no problems for the last 2 years.
Suddenly (and I mean within 10 min)
Everything died, a fire shrimp, mandarin goby, Yellow Tang, 2 Clowns, a Damsel, and possibly some crabs.  There was much horror and tears from my mother, I feel terrible but I also want to find an answer so this never happens again.
We took a water sample to Big Al's (big aquarium store) and they said that all the stats were clear and there was nothing that would have caused somthing that dramatic.  The tests they do are simple ph, nitrate, chlorine ect.  Their suggestion is that it may have been a pocket of Methane Gas, we were thinking that it was perhaps an electrical current, both seem highly unlikely but an expert opinion would shed some light on this situation.
So, this long winded message has two questions to it:
1) What possibly happend
2)Do you think my live rock will be ok? How do I tell if it's still alive?
Thank You so much on behalf of my family and my fish.
-Aisha

Answer
Hello Aisha. I am soo sorry to hear of your loss. I can truly say that I think what happened was some kind of toxin entering your tank. I don't think it was a pocket of methane gas. First you have to look at is whose hands were in the water. Was there anything on them?(lotions, detergents,Cleansing agents, anything) Also you have to look at what could have come in contact with the syphon hose.(where is it kept? is it near anything hazardous?could something have spilled onto it without you knowing?) These are all good questions to ponder. You may never know the true cause, however I am almost 100% sure it was a poisoning of some kind. As for your live rock I cannot be sure because I cannot say for sure exactly what got into your water.(Did you use municipal tap water? sometimes there are toxins that get into the city water supply that you don't know about that are at safe levels for humans but not fish)If you really must know than have your water tested professionally . I am sorry I can't be much more help. An electrical current would not kill your fish that quick!