I have had a water calla for so many years that I have a fair sized baby in a 5 gallon pail. It is better than the 3 foot wide original. I keep it in a small kidney shaped water garden in summer and, yes, there a few fish in the above ground pond. So my question is, why does the plant bloom in winter under lights? Too much nitrogen in late season or have I got a day light issue. I live in zone 4.
As with most bulbs, Water Lily's bloom once a year. They need a cool winter dormancy of at least 8 weeks to reinitiate their flowering cycle.
Each plant should bloom for about 2 to 3 weeks.
If a Water Lily does not bloom outdoors in a pond situation it is generally, not warm enough, not enough sunlight, or lack of nutrition. They can be few a tablet fertilizer for Water Lilies.
Without the cold period and the addition of artificial lighting, your Lily is confused!