Thoughts??
 

I've been away for 2 weeks and while gone, my 3 herbivorous fish died. No sign of illness or injury, all three at different times over the 2 weeks. I'm inclined to believe that some macro algae growing on the rock might be toxic or caused some other gut issue. All carnivorous fish are fine.
Anyone ever hear anything like this?

Not sure if this helps but I read a while back on Reef to Reef about a woman who lost her herbavoires to an illness that she traced back to her prepared food for them sorry don't remember a lot of the story but do remember it was her prepared food that caused it.

Same food they've been eating for a month in holding tanks.

no flatworms?

Nope. Nothing else obvious that I can think of. Slight cyano in the tank, but I don't think that would do it

Good to see you back Brad.

Just for a couple days, I have to head back over on Sunday :(

That is unusual. I would be curious to hear if anyone else has witnessed something similar.

What kind of herbivorous fish?

Herbivorous fish are like dogs while carnivorous fish are like cats. That being said... if you were gone for 2 weeks they could have died from loneliness. ;)

Nah, JJ spent hours talking to them :)

It could be a coincidence, but only the three leaf eaters, not any meat eaters. Weird.

I just pulled a bunch of this macro algae, and I doubt anything ate it. Tough as leather! My next guess is O2 depletion, pumps were at a low setting, plus some cyano and large plants to use it up.

If they all looked fine during the day and were active and eating well and came from established systems (not newly caught), and then just suddenly died overnight (when O2 is at its lowest), and your aeration was lowered during this timespan, then lack of O2 is a good possibility.