Hi, you can never really tell when the pneumonia will set in, the turtle will appear to be healthy and suddenly you will see symptoms... They are very tricky that way

. You can prevent it though by keeping temperatures proper, i.e. 75-78F water and 90-95F basking, the higher land temperature entices them to bask. Keep them away from drafts and cold air and hopefully there won't be a problem. If it shows signs of pneumonia bump up the temperatures a bit for a while.