I set up a refugium... it' s a HOB, small 19 inch in length - about 2-3 gallons of water. I have a PC light on it , with 50w light. I bought some chaeto and it's been about 2.5 weeks. The chaeto came really green and hard, now it looks like has some "dust ball" algea on it and is less firm...is this normal or is it dying? what can I do ?