Red patches on plastron could be signs of sepsis. Have you noticed any possible wounds? Is the tortoise being as active as usual? Does it have energy to resist when you pick it up?
What kind of enclosure do you keep her in? Temperature and humidity? What is she fed?
Could be some sort of metabolic bone disease, but we gotta wait for the smarter ppl to tell for sure.
I wouldn't advise on using mats as they don't retain moisture very well. Tortoises also cannot dig into it, like mentioned above. Which means that they cannot easily regulate the micro climates they are subjugating themselves to.
Ultimately, it probably won't kill them. I've seen tortoises...
Pictures of enclosure? What have you been feeding her? What bulbs do you use for the enclosure? (If you are using coiled UVB bulbs remove them immediately)
Can we get some photos of his enclosure? What have you been feeding him? What temperature is he being kept at?
Unfortunately, it isn't uncommon for people to buy pets before realising the commitment they are making, you are trying to give him the best possible chance, so beat yourself up over...
The water in the UK is known to be quite hard, so hard water stains could be a possibility. Try gently wiping white areas with vinegar and see if it comes off. All in all though, hard water stains usually don't have any negative effects to the turtle's health.
On the other hand, they could be...
For one they can compromise the structure of the skin, making it lose its ability to keep out pathogens as well as weakening the immune system. Therefore leading to a secondary infection from opportunistic microbes. As mentioned before they also connect themselves to blood vessels via fungal...
Fungal infections on the skin always connect themselves to blood vessels as it provides them with nutrients and makes it very painful to remove by force. It is better to let the medication to do its work as well as drying it out by forcing it out of water. I wouldn't recommend getting rid of it...
Like DoubleD1996! said, this is undoubtedly a fungal infection as a result of poor water quality. Do a water change 25% in your pond every week if you can. If any other turtles show symptoms of this infection, quarintine and dry dock them until it is cleared. I'm not a vet so I can't recommend...
It might be a yolk scar left behind after the yolk sac has been absorbed. In a younger individual this is normal and not of concern. However, considering that your Hermann's is already 5 months old, and the size of the mark, it might be an incomplete fusion of the plastron after the absrobtion...
Personally, I have stopped buying anything from any pet shop that sells any turtle species as there is no way I can confirm that they were not wild caught or abused. In case that they are wild caught, I wouldn't want to give my money to them so that they can continue doing stuff like this.
It...