The most useful information is missing from this post, and you may not have it. It would consist of his living conditions and care before his arrival to you. This could lead to insight on intestinal irritations such as particle tears, parasites or more underlying infections.
Either way, your best route is to obtain a fecal test.
Hi, his living conditions are good now, his substrate is calsi sand, uvb is 5% & a komodo day basking light 75watt, which are both on for 12 to 14 hours a day.
He came out of a slum had no UV light for months or a basking light, only an unguarded ceramic bulb, he was fed crickets just chucked into his Viv.

I'm assuming a by a fecal test you mean by a vet ?
He's active and bright eyed, very friendly, he's had a little bath today also noticed his back looks a bit scaly, kind of silver coloured, don't know if this is due to conditions he's been living in previously, any ideas?
Thank you for your help.

Krissy.