in my tenner. I thought it was looking lovely clean, because I took the trouble to scrape spot algae off the inside of the glass on friday. I hadn't realized how much there was, and it's really hard stuff. So I have to rethink the light- probably too strong still- maybe block it with layer of plastic or tape... or raise it up yet again. I'd hoped the duckweed would screen some light out, but it's not growing that fast.