Aside from the overhead costs of pizza the ninja turtles 🤣🤣. I like the painted turtles. I haven't had much interaction with any other species. I have saved countless turtles here in Ohio from death by car tire, but I don't know what species they were. One was a snapping turtle.
You still need to improve his living quarters for correct temperatures and anything else I missed from above. You don't want to write off that the antibiotics is a affordable easy fix. It's not a good practice to play the F#$% around and find out game with the well being of reptiles. The oil...
The part that I find concerning about the substrate you are using is this, sphagnum peat moss, extremely fine sand both can have a negative impact on the tortoise.
No it's a thermostat just like how you regulate the temperature of your home except this one is for your tortoises home. The ceramic heat emitter you have already plugs in the this to control it. Also I personally didn't have any luck using that housing with the ceramic heat emitters in it.
Can you turn up the temperature settings on the C.H.E's thermostats? From what I recall 2 of those should be enough to heat that size enclosure. @Tom is right about finding the cause and bringing up the heat.
On my little redfoot they had me hold one of his front legs out and put the needle in the area between his leg and neck. But they can take it through the mouth I believe if they are big enough. It's easier with 2 people
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terracotta saucers work best for Water and food dishes. It's textured enough for them to get traction to get out. Also make them level with the substrate also.
Hatchlings need heat and humidity to get a good start on healthy smooth shells. So 80-84 temps and mid 80's relative humidity. Higher temps in basking spot.
I would stick with the Reptibark. It holds moisture well and less chance of the tortoise eating it or it getting stuck on its food. Also it is less mess and easier to maintain.