Jinx, this doesn't surprise me one bit. Same thing happened to me. I had a DMPS IV test done and they tested my urine. Not only was it normal, I was so low in mercury they decided there and then that I was not poisoned.
However, the DMPS itself had unleashed so much mercury back into my system, I was a total mess. I had no sympathy at all from teh doctor who did it and he wanted nothing more to do with it.

So I was on my own and I believed in myself, I knew I was poisoned and basically chelated it out with other mercury detox methods. That with amalgam removal, finally got me better (then). No test has shown any level on me. One of the top doctors in my country Dr Mike Godfrey called this Retention toxicity. And if anything was not a good sign, but rather explained why I was so ill. He actually said he would have been happier to see higher levels of mercury, rather than the near nothing levels he found on me. Because even healthy people have levels of mercury, because in one way or the other, we're exposed. When the level shows very low, this is actually quite abnormal, which is why he called it retaining the poisons, rather than eliminating them. People who excrete mercury well, usually show higher levels than those who don't.

There are many reasons for low levels on testing, which is why they are notoriously inaccurate. Andy Cutler instead advises a hair test to test for deranged minerals instead. As he says there is a pattern that you can detect if mercury is at the bottom of it, though mercury on the hair test will usually be little, they'll be some classic other signs instead.

alongside this, one of the other tests is simply chelation. You use a mercury chelating agent, if your symptoms become exaggerated, that is also a high indication you've hit the target.

You already know this Jinx., you've tried it and look what happens?

So, you're not alone in this. I had a feeling the test would come back like this. It's typical and really frustrating. Those around you will not understand this senario either. I was lucky the top doctor here explained it to me. In fact, he was so concerned with the low levels, he said it was abnormally low. He said he wanted to get hte levels UP so that would show it coming out more.

I have listened to an audio tape from the US, with yet another top doctor in mercury detox. Paula Bickle I believe her name is. She described the same problem. She said in her experience, the sickest patients show the lowest levels of mercury. And she described them, how hard they are to chelate and how ill they are.

So how can mercury really be tested if that is the case? I dont think it can that accurately in most, unless it's a direct acute poisoning that shows immediate levels.

You could try the hair test. I can send more info on that and what to look for. But I really think you know the answer, your symptoms are exacerbated with the cilantro and ALA. That's telling enough.