dead fish unknown reason possibly bug spray

Question
we had a 15 gallon eclipse tank set up as a reef tank all was going well and we believe  bug spray was used near tank as we lost two damsels and a clown fish and one not doing so well we moved the living one to another tank and went to local pet shop he tested water and every thing was fine with exception it was a little low on calcium but not bad.  He thought we were suffocating fish which i thought was a little odd especially with a pump from eclipse pump ,a hydor 1koralia 1, and 1 air stone on pump. then we though toxic poisoning from bug spray the other fish we took out  was doing fine and revived in friends tank. we changed tan to 10 gallon with all the same did water change put clown back in it died within a day. called another friend he suggested new carbon and large water change we did so and let tank run for two weeks not loosing any snails or hermits we thought it would be safe we added a three lined damsel and it could not be found after an hour and feeding brine so we started looking and pulling live rock out of tank and finally found it stuck up in a rock nearly dead we have moved it to friends tank and are very frustrated as we don't know what to do now  hope you have some ideas. thanks

Answer
Hi Noel,
So sorry to hear about your losses and the issues you're having. Your inverts(snails, hermits, etc) are still alive? Invertebrate life is usually impacted first by pollutants or toxins. If this is the case, I would just do another HUGE(50% to 75%) water change and add activated carbon to the filtration(quarter cup for every 5 gallons), and let it run for a few weeks in this manor. Fallow, NO FISH OR NEW ADDITIONS.
However, in the event that the system was contaminated with a poison(bug spray), I would do a 100% water change, rinse the live rock thoroughly, get new filter media, add carbon to the filtration(quarter cup for every 5 gallons) after you refill the tank and let it run for a few weeks, fallow(no fishies). That should be enough to eradicate any bug spray residue. Check the can of the suspected bug spray, aerosol or a pump spray? Look at ingredients, time spanning bug killers usually have an oil base to prolong effectiveness. If this is the case, you may need to do a complete washing of the system(no soaps or detergents) in warm water, rinse everything thoroughly,  and let the system run for a month to a month and a half, fallow, with carbon in the filtration. I would also look around the tanks environment to be sure first. Make sure there is nothing else that may be getting into the air lines or the water somehow(air fresheners, sanitizers, cleaners, etc). I know, a pretty big chore, but unfortunately the only way you can be sure to rid the system of whatever(toxins, poisons, parasites, diseases, etc) is doing the damage. It would be easier if you knew exactly what the culprit was, but this is what we have to work with. I hope this helps, if you have any more information, I'll be glad to get you more specific details on dealing with specific pollutants and toxins. Let me know if I can help.