How to clean a plating bath?

I use a Watt's dull Ni plating bath and find the Ni surface plated with so many pits. The pits look shiny when viewed by unaided eye. But under microscope, it is a small dark hole, sometimes the Ni around the dark hole is also dark in color.

Concentration of Ni I use = 95g/L of Ni without additive.

With current density about 2.8ASD\

I have tried to use hydrogen peroxide and carbon filter to clean the bath over 7 days... but no improvement...

Is that using active carbon powder to clean the tank is the only method to solve this problem? Please help me.

Thanks for your kindly help.

Generally, hydrogen gas is evolved when you plate nickel. The hydrogen bubbles can adhere to the part, and when this happens, a pit is created in the electroplate. The most common way to prevent this is to add a commercial anti-pit agent (wetter) which will prevent the hydrogen bubble from adhering to the work.