r/algae

I have a small ten gallon tank currently that's been up for 2 months now. Its housing a betta, 6 corydoras, an assassin snail, and a few bladder snails. Everyone (besides the snails obviously) has been getting along well, they dont even acknowledge eachother. The tank is decently planted, I have a few bunches of moss, some swords, duckweed, and 4 or 5 other plants. Im planning to get more as I want this to be a heavily planted tank. Its got plenty of surface area to grow as the tank is cluttered with driftwood, spider wood, and large stones. I leave the lights on for about 15 hours a day, fertilizer every 2 weeks, do about 20% water changes every Saturday, and still the only thing close ive gotten to algae is a small bit of diatoms. This isn't meant to be a brag or anything, I really want some algae. I'd like to get some shrimp soon, and i dont want them to starve though i do have some shrimp granules. I also just really like the look of algae, I love the natural green look of it and ive heard it's beneficial in most cases. What can I do different to make some grow??