Splenda/Canderel?

I'm in the UK and I use Canderel as a sweetener.
I just had two disastrous attempts at a flourless microwave in a minute chocolate cake, the first was bitter and grainy the 2nd a little less so but that's because instead of 1 tbsp of Canderel I used 3.

The recipe called for Splenda but I only have Canderel. I really want some cake and i'm following low carb so really need this to work so before I mess up a third attempt is Splenda sweeter than the other? Is that what's ruining it or something else?

This is the link to what I was attempting.
http://cake-o-cake.blogspot.co.uk/2012/07/1-minute-flourless-chocolate-cupcake.html?m=1

All help appreciated.
Thanks
Serene

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