Similar experience here, but in a top coil clearo. Not all juices have the same effect, but after 6ml of some kinds of juice, I am left with a half ml of much darker stuff that is getting close to opaque. I can dump the stuff, clean the tank part and the coil/wick unit, and all is well. My coils and wicks are still fine for a repeat, but it does seriously shorten their lifespan. I have been keeping all this dark juice hoping I might be able to filter it. As an experiment, I put some in an carto I had already cleaned a couple of times and didn't care if I wasted, and it did vape. It didn't taste burnt, but it didn't make much vapor and also barely wicked through the filler material. I have no need to look at this junk through a microscope, it's obviously changed for the worse. Since only certain juices do this, it would be nice to know if a higher or lower resistance coil might do a better job on these problem juices. I would do this experiment myself, but I finally finished off the last of my problematic juices, and won't be ordering anymore of them, for obvious reasons.
Anybody know if there is any hope for this liquid? I suppose a centrifuge might do the job, but it might also separate the PG, VG, flavor, and nicotine. Like most people, I don't have access to a centrifuge, and I wouldn't go through all that trouble, anyways. It sucks when you like a juice but it kills your cartos or coils extra fast. Sometimes, when a thing won't work, you just can't fix it.