Just made the simplest UAS in the back of my de-rimmed Nanocube 28. I read that chaeto would just wash away in the back overflow chamber so I decided and think it is a better idea to put a UAS. I ruffed up the screen and am using a 5 watt led grow light. I am getting patches of dark green. The photos are of 2 weeks growth. When should I scrape some off?