It doesnt really matter what others have done, or tell you about doing. What matters is the facts that are specific to YOUR tank. Some people may have done what you have done and been fine, but since YOUR tank is not fine, you need to adjust the course things are taking.
Most people here feel you are in trouble and headed for more. Since you are experiencing the same things they are describing, it is only logical to react in the way they suggest.
Death and high levels of nitrites are proof that things just didnt work out the way that you think they could have. Its really just that simple. The experiment is pretty much over, and we can all conclude that it is unlikely that such a bioload can survive in a 30g tank, right?
Youve got the cash, so return them and chalk it up to experience.