My arrow leaf philodendron, a large floor plant, developed tiny yellow -turning brown (?) spots on all the leaves soon after I brought it home from the plant nursery. On the undersides of the leaves most of the same spots are sticky, some crusted over. The plant otherwise appears healthy, has not lost any leaves, and new ones are continuing to grow. They open up without yellow spots and appear healthy, but within a few weeks also develop these. I have isolated the plant and treated with a product called ORGANICIDE (92% fish oil) and have seen no change. Another web site opinion was that this is plant scale. There is absolutely nothing on the stems to show a scale infestation. Any second opinions? Treatment suggestions? Products to try?