Yes. A ULNS deliberately very carefully limits nutrients on the input. What you have is rampant Dinos that are eating everything like crazy, leaving no nutrients left in the water to detect. You see exactly the same with big hair algae problems, etc. Sad about the hawfish. You might want to check for ammonia. With dinos/etc dying, that might be up. I would suggest just restarting. Sounds like minimal livestock. For the rocks: Cleaning + bleach is step 1. I would soak those in tap water with vinegar (or muriatic acid) for a couple of days, to break up surface crud. Then soak in tap water + lanthanum chloride, to soak up phosphates. You need to eliminate the dinos, sure, but you also need to eliminate nutrients/etc from the rocks.