mass lily die off?

[Joshi83]

Ok, did Ph test and Ammonia Test, all came back perfect results.
I had the all too common oil slick happening too from the decomposing pads, so bucketed the top of the water off and did a 25% change of the water, treating it again after topping up.
Tested again and perfect results.
The lilies look fine at the roots, there are new pads forming at the base, but they are only small at the moment, which makes me worry a bit as my older lilies are sprouting pads but only small too and not surfacing and i would hate this new one to go the same way.
Hopefully with more regular feeding of the lilies they will grow bigger and stronger.

When i removed the dead pads today the stems were still very thick and strong.
I also notice the remaining pads that are slowing going brown are not floating on the edges, as in the middle of the pad is floating on top of the water but the outer edge of the pad is under water. the middle part out of the water is green, the edges are brown.

Still stumped as to whats going on...

 

[addy1]

from the net:

The leaves on a water lily will turn yellow and brown and eventually die off and get mushy, as part of the normal life cycle. But you should always see one or two new leaves for every leaf that dies off naturally. The black spots however, are not normal. Do you have water splashing on the leaves? Water droplets will magnify the sun and burn the leaves with little round holes.

Another possibility is that the plant is suffering a form of root rot. How deep is the top of the pot below the water surface? The flower buds dying off may be from the same reason as the leaves. So water depth is very important. Lilies need at least 10-18" of water over the top of their roots (or the top of the pot). If you pull out the plant and feel the roots, they should be firm like a potato, not mushy. If the roots are firm and the water level is correct, I would look at any products you are putting in the pond. Some algae formulas will adversely effect the good plants too.

Last I would look at nourishment, maybe you are under or over fertilizing the plant. Lilies are very heavy feeders and do best with monthly fertilizing (with an aquatic plant fertilizer tablet). It could also be a combination of factors such as parasites, rot and water quality. Water lilies do not like high pH, (over 9.0 makes some varieties go dormant).