Why does my turtle smell bad and its vent is always open? Is it sick?

Unfortunately, the "tumor" cannot be appreciated in the images provided. Consider an exam with your veterinarian or a vet experienced in treating reptiles. Also, decrease the amount of pellets being fed. Remove any uneaten food once the turtle stops eating. Offer a balanced diet consisting of protein (feeder fish, nightcrawlers, etc), fresh greens and vegetables and a small amount of commercial pellets. Provide vitamin and mineral supplementation as well as adequate UVB lighting.

Unless you have cleaned your tank with bleach (which you should never do) then it is probably due to the chlorine in the tap water. There are dechlorinating chemicals you can get from your pet store that should take care of that.

This can be due to poor water quality. Dirty water increases the risk of infection. Maintain water quality via filtration and regular partial water changes. Turtles need powerful filtration, so confirm your filter is rated for at least twice the volume of the tank. Infection should be confirmed by your veterinarian or a vet experienced in treating reptiles. This will require a physical exam. Prescription antibiotics can be administered or dispensed afterwards.

Shell rot is characterized by pitting, soft spots, foul odor or discharge or loss of scutes. It can be a serious condition and requires veterinary attention. Your turtle may have rot or the discoloration may be due to excess mold or algae. Clean the tank, do a water change and change the filter media. Confirm proper environmental conditions for your particular species of turtle. Try using a toothbrush and gently scrubbing the affected area of the shell. Make sure your turtle has a warm, dry basking area with proper UVB lighting. If your UVB bulb is older than 6 months, replace it. Do not place glass or plastic covers between the turtle and the UVB bulb. Feed an appropriate diet and dust food with a calcium supplement once a week.

If Tuti has a fungal infection, or any type of infection, she should be examined by a veterinarian. If you cannot find one experienced in treating turtles, see a small animal veterinarian who may be able to consult by phone with a herp vet. Check the water quality as well. Turtles need large tanks with powerful filtration to maintain adequate water quality. If not, bacteria and fungi can grow out of control and infect the inhabitants of the tank. You can request a consultation to discuss the case in greater detail and to discuss tank set up, feeding and husbandry.

The increased in urination and sort stool ay be due to an increase in fluid intake or eating succulent fruits and vegetables. The soft stool can also be due to intestinal parasites. Bladder stones are also possible and would cause straining to urinate which could in turn cause a prolapse of the penis. An exam with your veterinarian or a vet experienced in treating reptiles would be recommended. Bloodwork and xrays may provide a different. If indicated, your vet can provide supportive care (fluids, antibiotics, deworming, etc) if indicated. In the meantime, keep him warm. Consider increasing ambient temperature in his enclosure by several degrees. Soak him daily in a warm 50/50 solution of water and an unflavored electrolyte replacement fluid. Decrease the amount fruit being fed. Make sure he continues to eat though.

Take him out of the water. If he responds or retreats into his shell he is, obviously, alive. Have him examined by your veterinarian or a vet experienced in treating reptiles. If he is floating and lethargic, he may be sick. This could be infection, malnutrition or parasites. Confirm proper environmental parameters for the species of turtle you have. Low temps can affect activity in reptiles. Feed an appropriate diet, commercial pellets supplemented with greens and some protein (crickets, feeder fish, earthworms). Dust food with a calcium/D3 powder and a multivitamin. Provide a UVB lightsource to promote shell health. If you post a new question with the species, I can provide more specific care information and a care sheet for future reference. You can also request a consultation to discuss the case in greater detail.