As pointed out by others, if you have not done so, you should clean the skimmer. Reducing water flow might help, but it may also reduce the amount of bubbles produced.
However, you may not have an issue. A skimmer can only remove what is in the water. It looks like you have an under populated tank, that is at least somewhat established. You also don't seem to have any algae issues. There may not be much material to remove. If you test your nitrate and phosphate levels, and find that they are low, I'd say that your system is normal, and there is no large amount of material to remove. You need not do anything else.