@addy1 did you always have the lotus in a container that was circulated with pond water? If I try one I will probably have it separate from the pond.
I started with them in the pond in some big containers, they constantly blew over, mine are 4-5 feet tall when grown.
I then put them in individual big rope handle containers from Walmart, 5 containers in a 300 gallon stock tank. Then a few years later, tossed them all out of those containers and let them co-mingle in the 300 gallon tank. I have not added fertilizer for years now, do not clean the tank, it stinks if you stir it up.
The water comes unfiltered from the big pond, a hose T off the line feeding the bog, into a garden hose that waterfalls into the first small pond, the second one is the 300 gallon lotus stock tank.
follow the red line from the right to the small ponds............that is the garden hose path, then you can see the arrows showing the water flow into the smaller ponds, back into the big pond.
This is last years flowers