Massive over extrusion after changing firmware
Very wise to change the firmware of the stock Anet A8. The stock firmware does not have thermal runaway protection which Marlin Firmware does have. 

You should be able to print equivalent or slightly better with Marlin Firmware as you can tweak it better/easier than the closed firmware clone of Repetier that is originally loaded onto the board. My A8 runs perfectly fine on 1.1.9.

To identify if this is over-extrusion, you need to check out the settings of the steps per millimeters that are defined in your configuration.h file:

/**
 * Default Axis Steps Per Unit (steps/mm)
 * Override with M92
 *                                      X, Y, Z, E0 [, E1[, E2[, E3[, E4]]]]
 */
#define DEFAULT_AXIS_STEPS_PER_UNIT   { 100, 100, 400, 100 }


Furthermore, rather than calculating the flow reduction, you could calibrate your extruder.

From the images it it hard to say whether this is over extrusion or not, it does look like it is printed at a high temperature. Please update the question to include print material and print settings (hot end temperature).