Chick Emergency! Chicks dying mysteriously!

[DuckDuckGooseMum]

I bought Polish hatching eggs. Day 19 they hatched. Out of 22 viable eggs, 12 hatched between day 19-20. 1 died shortly after hatching in the incubator. They're 2 weeks old tomorrow and several days ago they started dying at the rate of 1 or 2 per day. I don't know why, but the Tolbunts have all died now except 1. Now this one looks bad as well. I'm scared and desperate to help them.
I am thinking it's likely a genetic issue because of the fact that all the Tolbunts have died except this one and the bantams are smaller. I have changed the box I keep them in. I was using paper towels and I replaced them with pine shavings and now with construction sand. I messed up on the feed and got an All flock type they loaded up for me and didn't realize it until about 3 days afterwards so at first I thought that was the problem, but I corrected that immediately and for 3 days they have had starter chick feed..organic. I add a pinch of chick grit and nothing more. I have given probiotics and electrolytes in moderation, but not over 3 days & now only water for 2 days. It's not temperature. I am monitoring that and it's perfect. The box is clean and they're not injured. I'm completely at a loss.
This chick is now showing the same signs the others did. Standing still, then it goes to almost labored breathing and no interest or little interest in food & water and then finally death. 1 chick I tried to save with forcing water with electrolytes but it didn't help and the chick appeared to be convulsing at the end and whimpering. I have Oxytetracycline for Poultry and I have some other antibiotics. I know it will die if I do nothing so any advice is welcome!

 

[Wyorp Rock]

I messed up on the feed and got an All flock type they loaded up for me and didn't realize it until about 3 days afterwards so at first I thought that was the problem, but I corrected that immediately and for 3 days they have had starter chick feed..organic

It's not temperature. I am monitoring that and it's perfect.

Standing still, then it goes to almost labored breathing and no interest or little interest in food & water and then finally death

I'm sorry for your loss.

Do you have any poultry vitamins? I would try Poultry Nutri-Drench, Poultry Cell or one that has Vitamin E and B1 in it.

Your temperature is perfect - what is that? Can you please post some photo of the brooder, the chicks and their poop?

An all flock type feed if fresh shouldn't be a problem unless the pieces are too large for the chicks, then either crushing it up or making a wet mash would be the thing to do. Either way, getting the chick starter is fine too.

With this being crested birds - hard to know - your problem may be genetics especially if you've lost all of one line, but there's so many thing that can cause a decline.