I think a big part of the problem is the habitat, as it is very different from the sort of environment these newts inhabit in the wild. Once you get the proper set up, this species is highly aquatic! Here is the care sheet for Hypselotriton orientalis (the species of your newt):
Caudata Culture Species Entry - Cynops orientalis - Chinese firebelly
I would like to point out the text found under the natural range and habitat section: "Researchers have described the natural habitat as “suitable water bodies at various altitudes, mountain ponds, small brooks, flooded fields in mountain valleys...” and "cold still ponds, wells, terraced fields, and ditches". Early researchers also stated “Always the water is cold and quiet, in the shade of grass, with a mud bottom free from stones, and the animals frequently swim up to the surface, darting back and forth actively.” Though this information is limited, it gives clear hints on how to approach keeping this species in captivity."
So, I recommend removing the gravel completely and either leaving the tank bare bottomed with no substrate at all or using washed sand. I have used both methods with this species and both work well. The problem with the gravel is not only is it not something the newts would choose to inhabit, but it works great at trapping debris and fouling up your water. Cleaning it usually entails removing all the gravel and rinsing well on a regular and frequent basis, thus disturbing the newt. More so than routine water changes do.
Also, I cannot stress enough the importance of live plants in your newt's aquarium. And a lot of them. Enough so that they block the back of the aquarium from view. All the hiding places reduce stress and assist in water quality, elements that will make your newt feel more at home in the water. I recommend plants like elodea and java moss. They will need a light source, but have low-medium lighting needs.
And fill up the tank with water. More water means more stable water chemistry, so add enough water so that the tank is filled to about 90% capacity. As long as you have lots of plants near the surface where the newt can rest on while it returns to a more aquatic and proper lifestyle, it should be fine. With lots of plants you won't need a filter so that will keep the water "cold and quiet," just like the description of their habitat. Do frequent water changes, though - aim for 20% water change per week. Make sure the water is cool and aged, though! No warmer that 70F, and cooler is better.
Here you will find articles on various aspects of newt care, including housing and water quality:
Caudata Culture Articles. Read and reread it all and ask questions if you need to.
A complete overhaul of your husbandry methods my be a little overwhelming, but your newt's health and quality of life will be greatly improved. And they really are so much more enjoyable when they elicit natural behaviors!
Good luck!
HJ
