disc harrow

I have a small 4 ft harrow. How much weight would you load up on it? I have been using a tub full of rocks but the bottom rotted out today and dropped all the rocks in my garden. I was considering using a 55 gallon plastic drum and fill it with water( about 400lbs) each time I use it but I don't have the fittings to plug up the top of it.
Wally

I used 4 plastic milk cases,2 on each side, and filled them with rocks from the garden.

What ever amount you feel like dragging.I put 100 lbs on each section.[400 total]Seems to do a good job.Kevin