You havent said what all is in your tank right now. Rather than a tang you may want to try a "sea hare" I have one in my tank..ugly but great algae eater. Invest in a test kit right away. You need to monitor your phosphate level. It should be zero. I would also suggest watch your feeding of tank. You may be overdosing it a bit with food which would raise your phosphates as well. How often do you do water changes. In a tank of that size you should be doing a partial change every week. 10 per cent. Good luck
