Out of curiosity, is this a pretty new tank? Those levels make it seem like it is still cycling. If this is the case, do not add a fish, especially not a tang. Wait until ammonia = 0, nitrite = 0, and nitrate < 20. This means your tank has established enough biological filtration to handle fish. The reason for your algae bloom is the high level of organic material right now. This will eventually go down and your clean up crew will eventually catch up. Also, I would try to get that pH up soon. Do you use pH buffer at all? It should be at minimum above 8 and ideally around 8.3.