Most people are not aware that many companies that sell potting soil in Singapore actually offer soil-less mixes (yup, most soil-less mix are "sterile", void of any form of fungi and bacteria (that means also no beneficial bacteria and fungi which are needed crucially in a healthy soil)
Even soil based potting mix that are sold in Singapore can have very low count of beneficial fungi and other micro-organism either to manufacture or storage conditions that are less than ideal.
Without a good population of Fungi, your soil will not thrive no matter how much organic fertilisers you put into your soil as beneficial fungi helps break down organic matter to make nutrient available to plants.
On top of that, Mycorrhizae Fungi is a specific type of Fungi that builts symbotic relationship with plant roots and extend the range of its ability to take in nutrients from a greater volume of soil that the roots can reach.
You can order Mycorrhizae Fungi Here and apply into your soil