Why wont My Iguana grow?

Brief：
Ive had my iguana a couple of years and he hasnt grown much at all. Were feeding him lettuce and hes in a large screened cage. We even use a vitamin s.. 

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I've had my iguana a couple of years and he hasn't grown much at all. We're feeding him lettuce and he's in a large screened cage. We even use a vitamin spray. Oh yeah, we thought he could use a little company so we bought a couple of small lizards and he ate them. That seemed to bulk him up a bit. Should we try crickets like we do with the chamelian?

I hope you are kidding. If you would have done any research at all you would know that lettuce has NO nutritional value whatsoever. And animal proteins cause RENAL FAILURE. Iguanas are STRICT vegetarians. They need collard greens, dandilion greens, turnip greens, mustard greens, watercress, parsley, butternut squash, carrots, and hibiscus leaves and flowers. Not just one thing but many things, in the wild they eat thousands of different plants.

Do not feed him spinach and kale because it is high in oxcalates wich bind calcium.

Bananas have an improper calcium to phosphorous ratio and shouldnt be fed either except maybe for a treat once in a blue moon. ONce a week calcium powder should be dusted on the salad.

Screen cages are BAD for iguanas. Iguanas can lose toes and toenails and they let the heat and humidity out.

Iguanas need 70 % humidity and they need a basking spot of 90-95 degrees. Never use hot rocks they cause thermal burns. They need a flourescent uvb bulb that emits 5% or higher uvb rays, many professional iguana rescuers use Zoo Med's Reptisun 5.0 and exo -terras Repti-glo 5.0. The bulb needs to be replaced every 6 months and glass and plastic filters out uvb rays so you have to make sure it is unfiltered.