HLLE?

I agree that it looks more like a battle between tankmates.

In an effort to decrease Nitrates, have you been feeding less? This causes territorial agressiveness when the Alpha Fish says, "There's not enough food in this place for all of us. You gotta go!"

My suggestion, as you may know , is to introduce live algae into a well illuminated, preferably an upper area in the display, which reduces pollution as it feeds. I have a big clump of Chaeto I'll give you for free. Chaetomorpha is not their favorite algae so it will last longer as a pollution reducer while they nibble on it.
Another suggestion is to completely cease feeding dry foods in favor of natural foods, i.e., Leafy greens, Nori and frozen meaty foods that are packed with algae, like Emerald Entree and Spirulina Enriched Brine/Mysis. These natural foods provide longer lasting time release nutrients which are better for the fish for a longer duration and at the same time are less polluting to the water. Feed just enough Nori that it is all eaten in an hour or so, otherwise the leftover simply adds to the tank pollution. Leafy greens can be left hanging on the clip for hours.

As I'm writing this, I realize that you probably know all this already, but maybe another reader can benefit.

Did you know that an electricity leak into the water is not eliminated by a grounding probe? The truth is, a Grounding Probe exacerbates and prolongs the electricity leak because the electricity is flowing through the tank water until it reaches and follows the probe out to ground. A true short circuit contact of a power wire to tank water sends 110 volts to ground. Because of the physics of electricity through salt water, there is not enough electrical current to trip the house circuit breaker, but plenty enough to stress tank inhabitants for days, weeks or months. This, even while a hobbyist that is insulated from the ground goes about happily working with his/her arms in the tank, totally oblivious of the slow electrocution going on around them.
Another way of explaining this is to say that a grounding probe creates an electrical circuit running right through the fish.

If stray voltage is suspect, it can be verfied with a voltage meter like this:

1. Unplug the grounding probe and make sure the other end is still in the water.
2. Place one lead of the voltage meter in the ground hole of the 110 power source vacated by the grounding probe, either the wall or a power strip.
3. Place the other lead into the tank water or solidly touching the ground plug end of the grounding probe.
4. Set the meter to detect 110 AC voltage. (If you have a DC Pump, check again with the voltage meter set for DC voltage)

If the voltage meter shows more than 40 volts of AC electricity or more than half the DC voltage of the DC pump, there is a problem. One by one, unplug each individual electrical device until the voltage drops significantly. That device is the culprit.

Hope this helps,
Aloha,
Mark