well my second aro just died i added stress zyme and a poly pad to the tank the carben filter hasn't been running yet i have them on 3 different canisters 2 for filter pads and one for media. as for the carbon being spent that would make since but how would the water tern that fast the is what im finding weird is the filters weren't even on when i took the tests and yes it take 30 to 45 minits to fill the tank but i was testing every few inches of water height and it was not changing the cem readings i have never seen this before. i have had tanks spike and kill fish but after one or two water changes the chem lvls would return . were in this case i just cant get it to drop