In early March, we first checked the condition of the tank.
When we opened the big lid, we were surprised to see the blackish shining surface. It was oily and sticky, 3-4 millimeters thick layer.
And two big holes were also found. One hole was just under the pipe inlet, may be the water dropping in made the hole. Through such holes, water may be run quickly without enough filtering.
We need to resolve two issues, oily layer and holes.
We decided just remove oily materials from the surface and keep it next to the wall not through away out of the tank.
For holes we decided to fill with sand and coconut fiber. Also we planned to set a wooden pallet on the surface where water dropping in.
Let us see how the condition will be the same in coming months.