Old pic before we took her to the vet : https://i.imgur.com/8CLngb5.jpg
So long story short, we got this terrapin (red eared slider) 20+ years ago and have been raising her mostly on land due to bad advice from the pet shop that we got her from. Recently, we took her to the vet because she isn't eating much or pooping much anymore for about two weeks. The vet checked her over, noted that she had a slight respiratory infection, some minor shell rot and prescribed us an anti-bacterial solution and a nutritional supplement which we fed to her with a syringe through her mouth. She also gave us a cleaning solution for her shell which is for the shell rot.
Other than that, she said the terrapin seemed OK and suggested we change her environment to a large water tank (at least 320l, more than 4 times her size) complete with basking dock and UVB light.
We feed her turtle pellets that are described as being enriched with vitamins and calcium twice a day, and the vet told us to just follow the feeding instructions on the package. These are the pellets : https://www.petloverscentre.com/product ... light-140g. We also feed her some dried prawns with the pellets.
I did ask if she had metabolic bone disease or anything like that as some people here said she did, but she said that the only way to check that would be to do a blood test, which would require her to use anaesthesia, and there was a risk that she wouldn't wake up afterwards because of her advanced age (she is more than 20 years old). We didnt want to risk that so we didnt do it. She did say that she didnt think the terrapin was in any pain but there might be some discomfort because of her deformed shell.
Now i'm not sure what to do with her. We have been feeding her the nutritional supplement + anti-bacterial for about a week now, but her appetite hasnt improved althoguh she does eat small amounts each day. I'm not sure if this is a sign of a problem.
I would like to try moving her to a water tank + basking dock + UVB light setup, but i'm not sure how to find a tank that is large enough. She is quite large, I measured her to be 28cm long from head to tail and 18cm wide. The vet advised us to use a water tank that is at least 320L large, i've tried asking pet shops but they don't seem to sell tanks anywhere that large nor are they measured in terms of litres, just the usual length x width x height dimensions. I also have a feeling that it would be quite pricey. The pet shops dont seem comfortable with recommending a size either, they want us to give them the exact dimensions of the tank we want to buy.
I tried putting her in our regular tank with lots of fresh water to see if she would like it, but she just started swimming against the walls repeatedly instead of sitting on the floor of the tank like she usually does. It also seems like she is floating to the top of the water rather than staying at the bottom. I cant tell if she is just exercising or if she doesnt like the large amounts of water because she is not used to it. I'm concerned that if I do get a large tank for her, she wont like the deep water and will just sit on the basking dock or try to escape from the tank because she has spent 20+ years mostly on land and in shallow water.