Good info from See above. I would reiterate to get it out of that “bucket”, which almost always have inadequate drainage/air holes. Plastic pots also cause
root circling, and many other problems like rot and overheating/freezing as they fluctuate much more than the ground. If it needs to be watered every three days, it is in much too small of a pot. I suspect it may be waterlogged and getting root rot. I find lifting the pot slightly to gauge its weight/saturation much more reliable than any instrument. It
should feel noticeably lighter before watering again.
Still, it really will not be healthy unless its in the ground or a much larger and better drained container. Given that a pear will need winter chill to fruit, I don’t see a benefit of keeping it in a pot (as one might with citrus to move it inside in winter). Make sure to uncoil any circling
roots and allow them to spread fully in a hole dug wide
enough to accommodate them, and just deep enough to have the root flare just above ground. It can be an irregular shape to accommodate roots of different lengths without unnecessary work and soil disturbance. Planting “proud” or high, is almost always better than too deep, unless its a plant that roots from the stem easily (tomato, elderberry, raspberry).
I would also make a
compost tea with the best compost you can find, and minimal microbe foods in it. Screen it through 400micron mesh to allow as many microbes through as possible without clogging the sprayer, and fully cover the tree and leaf litter below it. After letting the pot get light (meaning roots are getting air that they need as much as water) I would also water with a compost extract at the next watering and soak the roots in it at transplanting. This will give the tree a healthier microbiome to fight whatever disease it has. I was able to eliminate any visible leaf curl on two badly infected nectarines last year doing this.