As I posted last week, both plants started to strip the bottom fan leaves for nitrogen and nutrients. This makes perfect sense, as the perlite makes up 50% of the mix, after giving it some more thought. To remedy the situation, I ordered the Biobizz line, and both plants are now taking in 1 litre a day of the full Biobizz line recommended for All-Mix.
This immediately stabilised both plants, which then enabled me to take the advice from Atomik_water in the comments and raise the temperature in the room to 29°C, while the plants remained around 26–27°C.
Both plants are now receiving a DLI of about 55 and show no signs of problems under the current watering and nutrient regime. I therefore intend to keep things the same until they finish.