Well I didn't have much success with the Splendex tonight.
I made a batch of "Sweet PG" - 6 drops of Splendex in with 3ml of of PG. I then made a coffee blend that was fairly sure to be in need of sweetening. A mix of 3 coffee flavors, at about 20% flavoring with PG-based nic-juice to bring it to 2ml of ejuice, no VG at all. I vaped it a bit, 4 or 5 drops dripped, and it wasn't bad but could have used some sweetening.
I added 4 drops of Sweet PG, and vaped for a while (dripping), long enough to wash out the atomizer and make sure I was getting nothing but the new stuff. There was no discernable change. I added 10 more drops of the Sweet PG and vaped for a while - the taste was slightly weaker, but there was no discernable change in sweetness. So I added a full drop of Splendex to the remains of my coffee blend, probably 1.5ml at this point.
There was a change, but it still wasn't very sweet. It seemed to produce more vapor, but that could have been my imagination, or perhaps my Prodigy had achieved one of those "perfect vaping" moments. The taste of the coffee was reduced - though I could have been getting used to it by this point of the night. Nah, the flavor had reduced a bit. And there was perhaps a bit more bitterness.
So I added 2 more drops of Splendex. That killed it. It wasn't vaping much, it was more bitter, and the taste was reduced. The little batch went down the drain.
Looking back...
I think the first full drop of Splendex was a little too much, and that's why it turned a touch bitter. 1/3 or 1/2 drop would have been better, I think.
Sweet PG at 20 parts PG to 1 part Splendex is silly. 5-to-1 is probably a better point, and still easily measurable.
Sweet PG, period, is probably a waste of time. The Splendex bottle produces a mighty fine drop, and 1 drop of Splendex mixed into 4 or 5ml of ejuice is probably closer to ideal. But if you make 2ml test batches like I do, then a 5-to-1 Sweet PG makes sense.
My initial coffee mix probably wasn't correct, since it wasn't sweet but it certainly wasn't dull. It was, really, almost sweet enough. Perhaps a mix that is not sweet at all would be better, since this would allow the Splendex to change the sweetness considerably, thus making the difference more detectable.
I shall continue tomorrow. I think a batch with LorAnn Keoke Coffee will do it. If my memory serves, Keoke on it's own is fairly dull and seriously needs sweetening. I'll make a little 5-to-1 Sweet PG, so I can add a single drop that should add noticeable sweetening without reducing the flavor noticeably.
We'll see.
