[Ozric Jonathan]

Hi Johnny. I agree with Naturalis that your temps are a bit low, especially if the tortoise isn't eating well.

I haven't used that specific lamp but I have tried another make at that wattage and I thought it was feeble.

I don't like any of the commercial substrates and some of them have caused problems. If it has white bits in it, there is a possibility your tortoise has been eating them and that can cause digestion problems.