It does not help to have a high nitrate level. You will need to manually remove as much as possibe and then add a clean up crew to the tank. You also need to get your nitrates down. There are many places where these come from. Overfeeding, replacment water, fish waste and overstocking are a few.
The algea will feed of light, phosphates and nitrates. These need to be checked and fixed. Poor lights can cause blooms and when you add the other two, you have disaster.
Nitrates are wahts left when nitrites break down. Anaerobic bacteria is what converts nitrates. You need to have some way to house this bacteria. Rather it be a DSB or an abundance of LR you have to have it or none will be natrualy converted.
Water changes will help as long as your water source is not a problem.