You have a small tank with a small light over it, even if you had the full 9 watts effectively lighting the plant. The problem that you are running into is that the watts per gallon ratio implies that you could grow plants in a coffee cup with a night light. The ratio might be OK but the light intensity would grow nothing at all.There is a minimum amount of light needed to grow any plant. Until you exceed that threshold, nothing will grow. Once you have enough light to grow something, you can start looking at whether you have enough light for a particular plant.

It was my opinion, and I am no plant expert, that 4 1/2 watts of effective light is probably below that threshold. Dying plant leaves under extreme low light sound like not enough light, that's all.

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Fishless cycling