Water lily question

I recently introduced 6 fully grown water lilies to my 5000 gal pond. The leaves are starting to yellow and some have small brown/black spots on them. It is a full sun pond with a pump transferring water at rate of 600 gal per hour.




Pondlady sez:


 Water lilies need feeding every 10 - 14 days with Pondtabbs or other aquatic plant fertilizer.
They also like to have the 
tops of their pots at least 18" below the surface of the water and are happier even deeper. 
And remember, the outer ring of leaves gets yellow and needs to be pinched off periodically so the new leaves can grow.
Same with the flowers. They will open and close for about 3 days and then die. Pick them off immediately. Don't let them decay in the pond.
Pinch leaves and flowers off at the pot, not at the top of the water.
Oh, and water lilies do not want water falling on their leaves, nor do they want to be too near moving water. A foot or so away is fine.