Hey all. Very sad news indeed -- 2 clutches are lost

.
My pair laid another batch only a few days after the ones that hatched on 7/21 -- so I decided to experiement and see if the new fry (hatched on 8/1) would co-exist with the ones hatched on 7/21. Everything was going ok for the first 2 weeks. I lost a few of the younger ones with popped bellies. I was very very careful to get the extra bbs out of the tank once they weren't orange anymore so they must have been good hunters. Then --- after the older ones had completely morphed and got a nice orangey color --- they would go into a freak-out and then simply lay down and die

They would swim in circles or back and forth across the tank and then just sink on their sides. It was a horrible thing to watch
The little ones all died during morph -- I am thinking maybe they got bbs too early -- but they seemed to tolerate it very well until they were actually going thru morph.
I was able to get the very last older one in a small cup -- I put a few new bbs in there with him -- he didn't even make a go at them.
I was at first thinking the freak-outs were bbs-shock (how do avoid such a thing and make sure they get enough to eat at the same time?) now I'm wondering if for some reason they stopped eating. And -- I suppose it could have been a result from my experiement.
To make matters worse my pair have not spawned again. No changes to the tank other than a water change (finally

). Maybe they are giving us all a break for a while lol.
Any suggestions would be most appreciated. Hope you all are doing well. Thanks!
Note --- the 3 oldest ones are doing great!