Glad I've been a bit helpful.
As far as the range that fish can tolerate my honest answer is it depends on the fish. Some people throw fish right in to cycle a tank and sometimes the fish actually survives. ANything over .25 is erason for an immediate water change though. Once you get to that level you are starting to poison the fish. It's a toss up as to how long a fish can last. I would also stay away from starfish for a bit, they are notoriously hard to keep especially the linkias. I had one starfish and he actually disingrated leg by leg over a weeks time. Very hard to watch. If you want a starfish I would suggest the serpent stars, they are alot easier to keep and are pretty neat, some will take food right from you.
What did you add fishwise this time? Hopefully not alot or not big time messy fish...