I am stunned. How big a batch is that strong ale? So you did a decoction mash. At what temps? What was the expected FG? Because if you aren't careful with a mash like that you can end up with a very high FG, much higher than the recipe FG. How long has it been in the fermenter. My strong Belgians take a total of 9 weeks before bottling. Did you even get full conversion, according to the iodine test, I mean?
How big a yeast starter did you build? 5 types of yeast seems excessive but that is just opinion.
Now to the Dark lager. Ok, so you were putting 1.070 wort into your beer for priming. What was your target CO2 volume? How many GU's did you estimate to be needed to get there? I estimate that for a five gallon batch with a gravity of 1.010 you would need approximately 9 - 10 GUs. 1.070 wort can deliver between 10 and 15 GUs per gallon depending on its fermentability. Did you really put between a gallon and a gallon and a half of the strong into the dark? If not, you might have misread the hydrometer.
The problem here is that we don't know the ultimate FG on the Strong to know how fermentable the primer is that went into the Dark. If it is not very fermentable you will be safe from bottle bombs but will have sickly sweet beer. If good and fermentable then the beer could get dangerous. In general, krausening is done from the next batch of the exact same beer.
it wasn't really a decoction mash....some experiment that a byo writer came up with.
you do your first mash and sparge, and then use the runoff (no boiling before adding) to mash a second grain bed.
we did half of the base malts and all the specialty grain in the first mash, and the rest of the base malt in the second.
mashed at 154 F (30 minutes for the first one.....the guy who wrote the article said all the sugars and enzymes would transfer into the second mash, and full conversion would occur....1 hour for the second, followed by a 15 minute rest at 148 F)
the target FG was in the 1.020 - 1.030 range
it wasn't a ridiculous amount of each yeast, dave cultures from every batch he does, and then he'll blend his favorite similar strains (he's got 5 strain english blend, and a blend he made of safale wheat yeast,fleishman's rapid rise baker's yeast and sweet mead/wine yeast......i realise these three are in no way similar.....but the blend makes a tasty strong ale), and seperate the blended cultures into jars for his friends.....he's pretty good about splitting it up so that each jar is roughly enough for a 5 gallon batch.
so we made a 1 liter starter with that culture and a vial of super high gravity from white labs.
now the dark lager....
i have no clue how to calculate Target CO2
i always (up until now) just read articles and did online research as to how much sugar or dme to add (as for proper "to style" carbonation).... or (sometimes) i'd just use carb tabs)
so even though i do know more than most folks here aparantly think i do about brewing, i am clueless about carbonation.
anyway i read about fermenting with wort or krausen beer.....i was intrigued, so even though i did not have a formula for doing so, i used the idea in a pinch......in hindsight, a terrible idea.
