Is the nitrite reading 02 or 2 off the chart.
He's pale because of the bad water quality, stress can also weaken there immune system. Being pale can be stress or desease.
Water changes and increase aeration.
Also a pair of angels need 20 gallon tanks.
The shark need 40 gallon or more.
Shouldn't of bought anymore fish.
Due to adding more fish the water quality bad.