I'm also unsure that the changes really did anything as the original 6 didn't make it. There is no true comparison. Could've just been a bad batch of chicks.
I'd like to think that was the case but i lost one in our second batch too, same cause. That's when i really sat down and did a bunch of reading. I think high Ph water was an issue and that is really easy to fix but I think the bigger problem was that i was giving them too much Rice, Pasta and mashed potato as treats. They were getting a serving of one of them every day.
I found this about breads which i think pasta is in the same category:
"As you know, bread is made from wheat. Exactly how problematic wheat will be for your chicken’s digestive tract depends on the type of wheat and the consistency in which it is fed to your flock.
Certain varieties of wheat contain starches that are difficult for your chicken’s foregut to digest. Since these starches are harder to digest, it slows down their digestion.
It’s no secret that bread is high in starch, either. The starch can present a problem for your chicken and become a food source for gut bacteria to grow out of balance in the digestive tract.
When the bacteria builds up, it will end up presenting as a sticky stool. So, depending on the type of wheat and how much you give them, your chicken can end up having digestive problems."
https://henraising.com/can-chickens-eat-bread/
I was also giving them left over mashed potato and I found this:
"Chickens shouldn't eat white potato
I don't feed our chickens white potatoes. No white potatoes - either cooked or raw. The entire plant, leaves, stems skins and flesh are part of the nightshade family and contain the toxin solanine.
Solanine destroys red blood cells and can cause diarrhea and heart failure. It is sometimes killed by cooking at high heats, however boiling won't reduce the solanine levels.
Best to stay away from all parts of the white potato including the vines and leaves.
(Note: Sweet potatoes are part of the morning glory family, not the nightshade family, and perfectly safe to feed to your chickens.)"
https://www.fresheggsdaily.blog/2013/02/toxic-treats-what-not-to-feed-your.html
It turns out even too much tomato may even be problematic. I was not sure, so I just stopped. Kept to greens, feeds and made sure they were getting grit and at least some calcium.