I feed maybe once per week when my NOx is is acting up. Be careful. Most fish can go weeks without eating.
Look, before anyone gets the wrong itea, I'm not saying "don't feed". Every tank (system) is different. Every fish is different, you have to get to know what you're keeping, and also have to take into account what status your tank is at.
All I'm saying is be cautious... I'd rather have my fish be a little hungry for 3-4 days than be poisoned and dying from nitrates and ammonia due to feeding.
Try adding some chaeto or mangroves to the sump system. There are no negative effects (other than possibly Mg getting quickly used by mangroves) bu using these items so it is one of the very few risk free/low risk options out there. Many people can get you plenty of chaeto for free. You should not have to pay for it. If not, I will gladly give you some. I just am pretty far from you.
Good luck.
Take your time, find the source of the nitrates and go from there. Just my opinion.