Puzzling.
I don't have a problem believing you Sproket, but I would simply like an explanation, or details, as to what's actually happening.
You refer the problem to the "Dtek rad", but would it be safe to say that it would be applicable to any heatercore?
The aquacoil doesn't have any tanks...
It seems to me that the dye is actually the problem, where not only does it not blend with the water, it's also heavier than water, and will easily pool where it can.
So the fault would lie with the Dtek dye, not the Dtek rad
If that's the case, then the DTek dye would have to be composed of some kind of heavy oil. Does that jive?
I've been wanting to order the DTek dye, but the shipping costs make it prohibitive, when ordered alone.
This may explain why the dye doesn't always dissapear: if the rad/core is top-mounted, it wouldn't pool, at least not as easily.
[edit]*IMPORTANT*: this was only my view, and shouldn't be taken as fact! The oil may come from another, yet unidentified source!