Two clutches with overbites this year. Is it our new incubator, us, or horrible luck?

[Gemini Pythons]

I'm sorry to hear that you are having issues with your new hatchlings. Your incubation method looks fine to me. 90F is cutting it close, but, by my experience: close to lethality, not consistent/repetitive deformity.

Yes, we think we are going to lower temps. My boyfriend was the one who first began breeding, and his mentor told him to incubate at 90F. He always did because of that without issue, but we will reduce it next clutch to see if it helps anyway. At least we know that incubating within the 88-90 range is safe, so lowering temps slightly should be alright.

As you mentioned: It is possible that this is a genetic issue, but, I would not expect this unless one of each of the breeding pair adults was from the same seller.

Actually, the mother and father of Clutch #2 (the awful one) came from the same breeder, as did the father of clutch #4. The two males have had normal clutches before with other snakes we've bought from him though. Most of our snakes are from him as he is the same person who mentored my boyfriend when he started out. Unfortunately, he's also the same person who recently passed away.

Chemicals: Were the egg boxes disinfected prior to use? If so: With what?

We disinfect after each clutch with unscented dish soap and water, then F10 (spray, let sit ten min, rinse)

The Pearlite (how old is it, how was it stored: temp/humidity, could it be harboring toxic mold/spores?)

we use new Pearlite each clutch. That's an interesting idea though because one bag is good for two clutches, so the bag has been open for at least a month between clutches. We keep the unused Pearlite in a drawer, just sealed in the bag it came in. We live in a very damp climate though. We've never seen mould grow on the Pearlite, but you never know what it invisible in there.

The Water (was it distilled, if not, could this be a chlorine/chloramine/fluorite/bacteria contamination?)

It wasn't distilled. That being said, we've never distilled it in past as our tap water is very clean and safe to drink, and haven't had any problems.

The Follicle Development (What were the parents eating? Could the food have absorbed a toxin? If you raised the rodents yourself--did you feed them anything odd or did they chew on toys?)

We feed frozen/thawed that we buy in bulk from a local feed supplier (not pet shop. The people we buy from do nothing but breed feeder animals). We've bought from them for the past ten years with no issues, and largely because they put their animals to sleep using oxygen deprivation, not gas (or electrocution). The mother of Clutch #2 was off food a long time, and I recall someone else who had posted here said the mother of their bad clutch has also been off food for awhile before she ovulated. The mother of Clutch #4 though fed exactly as you'd expect the feed/breeding cycle of a female ball python to be.

Anyhow, just a few thoughts

These are fantastic ideas, thank you so much for taking the time to write this!! We're going to lower our temps next clutch we have, and examine our Pearlite more closely. Thank you again!!