Hello. I currently have a nano 15 gallon reef tank for about 6 months. I only have soft corals ( zoanthus, mushrooms, pulsing xenia, yellow polyps, GSP, leather umbrella and green kenya three. That Last two ones are looking bad since the day i purchased them. The zoanthus is doing fine and growing as well as the yellow polyps. But the pulsing xenia stopped pulsing (and growing), the mushrooms do not grow as well and one of them has a lack of colour. Any thoughts about what is causing that problems in just some of my corals?