… I seem to remember the old Mr. Malty yeast calculator telling me I needed between 180ml and 200ml of lager yeast slurry for a 1.050 lager. Poke holes in that concept if you like... I have no idea if it still holds water. …
Not poking holes… just converting it to “WYeast”:
Ales with a specific gravity < 1.064 (16 °P): pitch 1.0 Kg (2.2 lbs) of thick slurry (40% yeast solids) per 1 BBL (1.17 hL) or 1 Liter (1 quart) of thick slurry per 1 BBL (1.17 hL)
Lagers with a specific gravity < 1.064 (16 °P): pitch 2.0 Kg (4.4 lbs.) of thick slurry (40% yeast solids) per 1 BBL (1.17 hL) or 2 Liters (2 quarts) of thick slurry per 1 BBL (1.17 hL)
High lagers with a specific gravity > 1.064 (16 °P): pitch 3.0 Kg (6.6 lbs.) of thick slurry (40% yeast solids) per 1 BBL (1.17 hL) or 3 Liters (3 quarts) of thick slurry per 1 BBL (1.17 hL)
Ref:
https://wyeastlab.com/resource/professional-yeast-harvesting-repitching/I believe 1 US BBL ≈ 31 US gal. 1 US Qt ≈ 32 US fl oz. So, ~ 1 fl oz per gal Ale harvested yeast slurry and ~ 2 fl oz per gal Lager harvested yeast slurry < 1.064. ~3 fl oz per gal harvested yeast slurry > 1.064 to meet the WYeast Professional recommendation.
I have had good results with this recommendation.
To meet this recommendation, Ken will need a little over 3 more oz of slurry in his lager in a 5 gal batch < 1.064. (200 ml ≈ 6.7 fl oz)