Just because plants don't pearl it doesn't mean they' re not healthy. It just means your water isn't super-saturated with water. Don't look to pearl as the number one sign your plants are doing well, as it may lead to unnecessary disappointment. Also it would probably help if you injected CO2 into your tank. As if you have lighting above 2 wpg the plants need more nutrients or else they will starve. Higher lighting makes them work harder and faster, so the run out of nutrients. When you get into high lighting tanks, you have to start dosing macro and micro ferts on a stable schedule. Also CO2 injection will help keep algae away. In a tank your size, 20 gallons, you could still do diy CO2 with good results. However, it seems you only have anacharis which pretty much grows anywhere( exept in my tank) and an amazon sword, which will probably soon outgrow your tank. Seeing as you haven't really got a fully planted tank I wouldn't worry. Just a question, but why do you have such high lighting on your tank? If you need me to elaborate on anything just ask.