new stock tank pond- water lily dying
I'm attempting to create a stock tank pond, and I could use some advice. I bought a sheep trough 2X6X2 from a farm store, and since it was kept outside at the store, I didn't scrub it down or disinfect it, thinking that anything on it that might harm plants or fish would have already worn off. I filled it with rain water from a rain barrel and let is sit for several weeks until I made it out to the pond store. Now I have two plants in it, one is considered a marginal (can't remember the name), and it seems to be doing very well. But, the water lily is really struggling. The bigger leaves started getting yellow and splotchy, so I have been removing them, and since it was putting out new leaves, I was not worried. But, now the new leaves are looking bad, too, and there are what looks like bites taken out of some of them on the edges, though I have not seen anything eating the leaves.
The water is fairly clear; I can see to the bottom, and the bottom and sides of the tank are slightly "dirty" looking, which seems to be normal. Curiously, I never really see bugs or butterflies or birds around the water, so I wonder if the water is somehow toxic? But, I have found mosquito larvae swimming around before I put in a mosquito dunk, so I'm thinking that it can't be all that bad.
Did I do something wrong? Do I need to empty it and scrub it out? Do I need to put in another plant to help with the oxygen? Thanks!