There was a bad batch of Carbon

http://www.advancedaquarist.com/blog...or-reef-carbon

i dont think the temperature or high salinity killed the fish !
cuz i have had a 29g bio cube too , my salinity been up to 1.030 and ( 84F ) my fish and coral were always fine

when my water temp went high i put Ice in my the back of my tank lol it worked
and check ur PH sometime it could drop fast to low and kill ur fish and coral

and i put fish coral in my 2 days old RSM250 all the fish and coral are fine

if you need help let me know im by surrey central

Another big one to check is Alkalinity. If there was a larger ALK swing, it can affect everything in the tank as well.

Also, get an RO/DI unit when you can. It will save you many, many, many headaches. .25 for PO4 will cause nothing but problems with coral growth and algae. Best to run GFO in a reactor to help reduce that dramatically.