Thanks, the pic helps. Do you only have one fish? If so, then it’s definitely not going to contribute much nitrogen to the clam or corals and you’re always going to be nutrient limited. You’re simply not running the light strong enough, given the appearance of the zoas (fluted and elongated). Also, if you’re just running the blue spectrum, it’s not going to cut it with a clam, they need a “fuller” daylight spectrum, with a lot of intensity, especially a maxima. Your skimmer is small, the reason it’s not pulling anything Is because there’s nothing for it to remove. I would keep it going, but feed your fish more throughout the day and also consider feeding coral foods and particulates to increase the nitrogen content.
If you haven’t done so already, I would buy James Fatherree’s book on clams. You can find it through this link
here.