I share a pond in Central Iowa that is approximately one acre in size. It was stocked a couple of years back by my neighbor with grass carp, HBG and BC. I have seen zero evidence of BC and have caught a significant number of palm sized and larger HBG all Spring and early Summer. We had a fish kill in late June due to two weeks of 100+ degree temps and the aerator was off during this time. All the grass carp died and I saw hundreds of fish wash up on shore, but I saw virtually no HBG wash up that were of any size. They were all finger size; some a little larger, some a little smaller. Since the kill off, I have not been catching anything. I am still seeing tons of smaller HBG, but still no HBG of the size I was catching all spring and early summer. Surely they are still alive since I didn't see them wash up??? Why are they not biting? I also bought a bag of fish feed from the Supply store and was only seeing the fingerlings eat, a ton of them came to the table.
So assuming the BC didn't make it, knowing all the grass carp are dead and concluding there are only HBG in the pond, what species, how many and when should I restock my pond? I would also be open to any other advice you might have for a new pond co-owner.
Oh, I should also share that the pond is more than 15 years old and my neighbor said it is approximately 18 feet deep ---at least it was before summer drought. After a fish kill three years ago the aerator was installed. I have only lived her one year so I don't know a lot more about the pond. The aerator is now being ran constantly and the water quality seems great. Thanks!

Can you post photos of the HBG you are catching? Curious if they are in fact HBG or another sunfish species or combination there of.

In ponds less than a couple areas in size, I like a HBG/HSB/CC combination. You could add 25-50 CC and 10-20 HSB to the pond. That should help control the reproduction of the HBG. Pray the BC are dead and do not reproduce. If they do, you'll have a serious management challenge.

I have been told that the HBG are Largemouth BG. I will try to post a photo if I get a chance.

I admit that I am apprehensive about HSB because I have been told that they do not reproduce. Wouldn't LMB be better, knowing they will also keep the HBG population in check and will also reproduce so I do not have to keep restocking?

I do have romantic visions of catching a 4 pound bass in my backyard. :-)

HBG won't produce enough fry to feed the LMB. HBG are "large mouth" bluegills, but they come about by crossing GSF and BG. No LMB involved....

The largest fish die in an environment that is low on O2, that's why you saw the GC dead. I'll bet the largest HBG are dead as well.

LMB and BG in ponds less than an acre often leads to very difficult management issues. Put and take fish like HSB, CC and HBG work best because they don't reproduce much and have to be restocked. You can closely control their numbers... The cost of restocking every couple years isn't that expensive and they're easily sourced.