Schism
Aquarium Advice Addict
If chemiclean killed livestock its very likely the directions weren't followed. The reason was probably lack of oxygen, if you place airstone in sump, point power heads at surface you will be fine. Chemiclean will not fix the problem however if you use it and immediatly follow it with GFO the GFO can out compeat it and absorb the PO4 before the cyano and fix the problem by reducind PO4 in the tank.
Directions were followed, airstone was used and waterchange done in each instance that i witnessed. I also had a buddy that used this product in his 380g shark tank, he lost all his fish and i seen it with my eyes. I also know a coral farmer that i buy from who used it on a reef display and lost about 40% of his livestock fish and coral.
Now when you throw in all the other cases of people who misread the instructions or do not apply them to the T then you will begin to see how Chemiclean is not exactly completely safe.
PO4 can be bound to other things besides cyano, and freeing it up into the water column rapidly can cause just as many problems. Not necessary. Its just my opinion and experience thats its much harder to replicate the ocean with chemical products.