DIET - A high fiber, low protein and calcium rich diet will ensure good digestive tract function and smooth growth.
as you say he is quite old im guessing from his diet he is not in good shape
The best diet by far is a selection of leafy material. Dandelions leaves and flowers, plantain, chickweed, flat lettuces, cabbage and others are all good examples. Please note that flat lettuce and cabbage should only be given in limited amounts and variety seems to give the best results. All food should be lightly dusted with a calcium and vitamin powder, of which there are a number specifically designed for herbivorous reptiles.
Horesfields are relatively problem free provided they are kept and fed as described- obiousley this is not the case, i would recomend bathe him in luke warm hand water like you would bath a baby in for 10-15 minutes he may not like this is he hasnt been bathed before pick some dandelion and washing it off, when he has had his bath offer him the food and see if he will take it, if not just keep spraying the dandelion to prevent if from drying out and persist,
other thing i could suggest is,this may sound crule, dont feed him for a day and then offer him the weeds he wont start him self dont worry,
the only think i am worried about is the tube feeding if i read it right you said he has only been tube fed since the op?
is this because he wont eat or because of otehr problems?
i would try that with the weeds tho first,
u have pm