Fluid ToolTip

How would I draw a Tooltip over a certain area to show the current fluid amount.

I tried doing

@Override
    public void addToolTip() {

        if (mouseX >= 15 && mouseX <= 30 && mouseY >= 18 && mouseY <= 75) {
            tooltip.add(tile.tank.getFluidAmount() + "/" + tile.tank.getCapacity());
        }
    }