Thank you! I’ve hopefully added a picture. I suspect that you’re right - every time I mention the plants my wife rolls her eyes….
I’m leaving the flower pot until it feels light, then watering well, and the water drains freely. The top layer of soil currently feels “sticky” after being watered a day ago - I also check that the top 1-2 cm is dry before watering. I’ll resist any further fertilisation unless the photo makes people think there’s a nutrient problem.
Thank you for the detailed reply - I’ve previously had no problems with “normal” plants but it really does sound like I’m killing these with love. Very, very jealous of your beast!