Hi. What did he weigh previously? What is the rate of weight gain over time? How long have you had him?
I see some problems here. The way to get him growing and thriving is to optimize your care and housing routines. The following is intended to help you improve things. Please don't feel attacked or insulted in the least. If no one points out what is wrong, you won't know what to fix. Most of the care info out in the world, on the internet, from vets and pet shops, is all old wrong out-dated info. I'll link the current and correct care info for you at the bottom of this post. Read through those two threads, and please feel free to ask ALL of your questions. Our only goal is to help you and your tortoise.
-Where is is 28C? There are four temperatures to monitor and adjust if needed. Warm side, cool side, basking area, and overnight low. SO where is it 28, and what are the other three temps?
-Topsoil is not a good substrate to use and possibly not safe.
-There is no way humidity is 91% with an open topped enclosure. That can't be done even in tropical humid areas. You might need a different hygrometer, or it might need to be placed somewhere else. Are you using the stick-on dial type from the pet store? Or a digital one from a hardware store?
-Spot type bulbs should not be used over tortoises. They are too hot and focus too much desiccating IR-A into too small of an area. Get a flood bulb. Arcadia makes and sells them in the UK.
-Those cfl type UV bulbs are ineffective as a UV source and they sometimes burn reptile eyes. They should not be used. If that bulb hurts your tortoise's eyes, it could very well make him stay hidden more of each day and spend less time eating. That could be a contributing factor. Get rid of that bulb and replace it with an Arcadia HO 12% tube.
-Hydration is a critically important part of health and growth for babies. How often are you soaking? What type of water dish are you offering?
Here is all the correct care info. As you read through these two threads, you will see some changes that you need to make, to help get your little one growing more:
Hello and welcome to tortoiseforum.org! We are all glad you are here! There is no other forum like this anywhere. We have tens of thousands of members from all over the world ranging from kids with their first tortoise to people who have been breeding and keeping high end tortoises since the...
I chose the title of this care sheet very carefully. Are there other ways to raise babies and care for adults? Yes. Yes there are, but those ways are not as good. What follows is the BEST way, according to 30 years of research and experimentation with hundreds of babies of many species. What is...