Those S. repens are looking good.
I have some newly planted in my 12 inch cube (Valentine's tank) that are also doing well, so am pleased to see the same for yours.
As for the slick on the surface, I think that dropping in fish food causes it as much as anything else. If there is the slightest bit of oil in the food (and there should be, since there is fat and oil in good quality insectivore or fish based fish food).
I think it is perfectly normal, although not ideal, since it can affect gas exchange. You can easily deal with it in one of two ways. Either drop a piece of kitchen towel paper onto the surface and lift it out (the grease will stick to the paper), or you can use a hand held jug rather than a siphon to do a partial water change. As the jug fills, the surface film will slide into it. Both methods are very quick and easy. :)
: 70litre mature setup; betta, purple rasboras, 2 nerites, amano and wood shrimp. Heavily planted.
: 22litre cube; betta, 2 amano. Heavily planted.
: 57litre cube; betta, ember tetras, 2 amano, 1 nerite, heavily planted.
; honey gourami, cherry barbs, green neons, kuhli loaches, otocinclus, pond snails and 1 assassin doing his thing. Heavily planted.