Why are do money tree's leaves turn yellow it has been watered once a week and placed beside the window How can it be made healthy again?

Yellowing is called necrosis. It is deprived of one of its essential nutrients. Depending on how the leaves are yellow will tell you what it is missing. Iron and manganese are popular nutrients that plants are missing. It would be a good idea to get a 10-10-10 fertilizer and mix it into the soil.