In my experience, my carambola was looking similar when it was indoors over winter, due to an infestation of spider mites.The mites were clearly visible, though back then the plant was rootbound, kept on the drier side and not fed. I think yours could be getting too much sun also, exactly as is mine now in the greenhouse. For me too much sun makes their leaves grow evidently smaller compared to a tree thats shaded.
As for the crystals I have always wondered what the hell are they.....I had alot of them forming on the non hardened wood and leaf petioles. It seems that if the plant stays dry for an extended period of time ,they accumulate ,and now when it gets artificially rained on by my mist system ,there is none of this stuff.