Could you please provide some of the details we requested. We cannot provide any help or explanation if you don't tell us about the tank.
However, if you mean that your tank had a nitrate reading of over 200 for any length of time, then that is definitely the killer, in addition to the ph being extremely low, it needs to be 8.0-8.3.
Once again, how many fish did you have in there? Two clownfish is already very overstocked, and if there are any other fish then the reason your clowns died is that you were so overstocked that the tank could not cope with the amount of bioload you subjected it to.