At least 10 lbs per canopy leg is recommended.

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Easy DIY tip: Many tall canopy sandbags can accommodate 2-liter soda bottles instead of loose sand.                                                                      Pouring and transporting sand can be messy, so....

                        A 2-liter soda bottle, when filled with water, weighs 4.4 pounds.   
                        A 2-liter bottle of sand is about 8 pounds - 2 on each leg would be more than enough.

                        A 1-gallon jug of water weighs 8.3 lbs.
                       

Even easier:  Dumbell/barbell weights and zip ties!

More complicated DIY tip:  a soda bottle filled with quick-set concrete will weigh even more.  An eye bolt inserted in the bottle                          opening as it dries allows the weights to be hung from the corners.

"Let's make it a project" method:  DIY Canopy Weights - Create Whimsy