Hello and sorry for your frog's death Charlie! Did veterinary performed a necropsy to try and find out what was problem with sick frog?
Next time an event like this happens, keep frog quarantined in hospital for at least 30 days or until receive a clear health report from vet, before returning to enclosure with other frogs.
Just to make sure all is well in enclosure, please review the care article (Frog Forum - Fire-Bellied Toad Care and Breeding - Bombina orientalis and relatives) and make sure their requirements are met. Also, recommend keep a watch on the remaining frogs since they shared the enclosure with sick one after symptoms manifested. If see anything abnormal in remaining frogs, please answer the questions below and we will try to help. Good luck!
1. Size of enclosure
2. # of inhabitants - specifically other frogs and size differences
3. Humidity
4. Temperature
5. Water - type - for both misting and soaking dish
6. Materials used for substrate
7. Enclosure set up i.e. plants (live or artificial), wood, bark and other materials.
- How were things prepared prior to being put into the viv.
8. Main food source
9. Vitamins and calcium? (how often)
10. Lighting
11. What is being used to maintain the temperature of the enclosure
12. When is the last time he/she ate
13. Have you found poop lately
14. A pic would be helpful including frog and enclosure (any including cell phone pic is fine)
15. How old is the frog
16. How long have you owned him/her
17. Is the frog wild caught or captive bred
18. Frog food- how often and if it is diverse, what other feeders are used as treats
19. How often the frog is handled
20. Is the enclosure kept in a high or low traffic area
21. Describe enclosure maintenance (water changes, cleaning, etc)
For Aquatic side (if more than a dish):
1. Tank Size and volume of water in it (full, 1/2 filled, etc.)?
3. Water source and any conditioner treatments?
4. Water Temperature and how is it heated (if so)?
5. Water chemistry levels: pH; Ammonia (NH3); Nitrites (NO2); Nitrates (NO3)? Note that if you do not have test kits, most aquariums/pet shops will do complimentary tests if you take a clean water sample.
6. Describe any filter system including model and media?
7. Substrate type?
18. Any medications in the water (treatment dosis and for how long)?
19. Any salt in water (how much)?
21. Describe tank maintenance to include water changes, cleaning, media changes, etc.).
By Lynn(flybyferns), GrifTheGreat, and aquatic questions added by Carlos(Mentat)