Duck starter crumbs alone should only be used for 2 weeks maximum. Gradually introduce some duck grower pellets, with a lower protein content, until the ducklings are happy with 100% grower-size pellets.
NEVER FEED DRY FOOD WITHOUT WATER. DRY CRUMBS WILL SWELL UP INSIDE THE DUCKLING WHEN IT DOES DRINK, AND IT WILL DIE.
Note that the protein content of 15% (for growers) is still too high. Runners can develop rough wings if they are forced too quickly on high protein food. Introduce wheat into the diet by 5 weeks—and provide grit. You can raise wheat to 50% of the diet by 10 weeks.
Runner ducklings need space and exercise to develop strong legs. Do not 'hot house' them too much but do protect them from wet weather. They have fluffy backs until up to 5–6 weeks old.
Continue with duck grower pellets and wheat (50:50) until they are 16 weeks-old. Then switch to a layer ration. Young ducks can come into lay at 24 - 26 weeks (occasionally even earlier) and will then need layers' pellets. Drakes can move on to more wheat in the diet after 16 weeks.
