30 gallons should be fine for a Powder Blue but not for all of your fish. 55 gallons would be more ideal for all fish but also add multiple powerheads as well because the Powder Blue requires higher flow rates, even in QT. I have a Powder Blue Tang who recovered 110% from Ich and is now very fat and healthy. I placed my Powder Blue in a 29 gallon bare bottom quarantine aquarium. This aquarium was equipped with a Maxi Jet 1200 power head, Red Sea Prizm Skimmer, 15 watt UV light w/ Mag 3 pump and a 100 watt heater. I performed 3 gallon water changes every three days. I used hyposalinity treatment for 6 weeks at 1.010ppm salinity. It took me a about five days to reduce the salinity from 1.025 ppm to 1.010ppm (go slow to not stress the fish). It also took me another week to gradually increase the salinity back to normal levels, so the fish stayed in the quarantine tank for a total of two months. It is very important to use a refractometer to measure salinity levels and also to check pH daily and add buffer, when necessary ( I used Kent Marine SuperBuffer dkH). I also maintained the temperature at a constant 82 degrees. As for food, I attached a lot of green algae seaweed to PVC pipe connected by rubber bands daily. I also fed the fish Formula One mixed with frozen brine shrimp soaked in Selcon and Kent Marine Zoe (liquid vitamin complex) daily as well. In the meantime, the system I returned the Powder Blue tang to remained fallow for two months, which is highly recommended to make sure Ich is no longer present in your main system. I hope this information is helpful. It worked very well for my Powder Blue Tang.
