They enjoy light, just not bright light is all. By adding tall silk plants, you help reduce the amount of light which makes them more comfortable. You can also add a tannin source to help stain the water darker (don't worry, comes out with a water change if you don't like it--it's beneficial to the fish though!). Either a piece of Mopani Driftwood will do or Indian Almond Leaf/Catappa leaf. Or you can get Rooibos tea, it's herbal and so thus no caffeine. Don't use just any tea though, caffeinated tea is bad! No de-caf tea either.