A safe indoor method I've used to control aphids and scale is rubbing alcohol. Either wet a cloth and wipe away the bugs, or use a dilution of alcohol and water (50% or so) and thoroughly mist the leaves. I try to avoid getting any alcohol in the soil while I do it, but I don't think it makes a huge difference to the plant; I just don't want to kill any of the soil fauna. Misting won't get them all, but it makes life hard enough that they don't really spread much if you do it once or twice a week. Especially for intricate, leafy plants like D. capensis, it's a valuable way to keep pests under control until the plants can be taken outside and a systemic insecticide applied.