Struggling with Water Lily — would appreciate advice

I want to be honest: I'm not getting great results with Water Lily and I'm not entirely sure why. frost damage on tender varieties left in shallow water has been a recurring problem despite my attempts to address it. I've been focusing on dividing overcrowded plants every two or three years in spring based on everything I've read.

cooling visual effect and microclimate benefit in summer is there in glimpses, which tells me the plant has potential in my conditions. I have it in an indoor water feature with appropriate species which might not be ideal. peak flowering period in midsummer showed some improvement. Two stars for now — not the plant's fault, but not a success yet. I'll update if things improve.