Shell of the turtle is progressively darkening

Question

I have one baby red eared slider. I got it a month ago. It's color was green when I got it, but now the shell color has starting become darker and also blackish. I understand that the color changes over time but is it normal to happen within a month.

Also, I noticed that shell is relatively soft at the top and bottom of the shell. I can press it down at the both edges. Is this softness normal?

The turtle is very active and no signs of the illness. It eats normally and always excited for food whenever I feed him.

I have ordered the UVB bulb and may get it soon. But is the MBD develops in a single month's time?

Answer 1

The greenish colour of your turtle is a sign of algea growing on the shell. This happens if the turtle could not get dry once per day.

The soft shell is sign for not enough UV-B light.

Like trond hansen wrote, most turtles go to a warm dry place in direct sunlight once per day (for some hours if not disturbed) to dry and warm up. The drying protects them from algae and bacteria growth. The sunlight enables them to produce some vitamins, which in turn enable the hardening of the shell. These vitamins aren't present in food. In food there are only the "building blocks" to build these vitamins of. In general, the warmth helps to use all parts of the food in stomach and so on.

The sunlight/basking light enables your turtle to produce vitamin D and some "feel-good" hormones.

The vitamin D is important for your turtle and helps with the uptake of calcium from the food.

If your turtle hasn't enough vitamin D it will start losing calcium from the body, even if the food contains the right amount of calcium.

Source: http://www.reptilesmagazine.com/Common-Diseases-Of-Aquatic-Turtles/