It doesn't neccesarily mean he will read them. You are right in saying that. However he has a better chance of reading info like this if he has it available to him, and that's where you come in. Also by giving him books and encouraging his learning (even if he doesn't read them) you are more likely to be asked questions.
It's all about being tactful and taking your time.
Also don't tell him what he can't have, instead try suggesting different options/combinations.
If he likes to buy fish maybe you should encourage a community tank. maybe then he would feel like he has enough fish, and you also get the chance to plant it.
Remember though that some people will always be stuck in their ways, it's incredibly frustrating but that's life.
Also he may have reasons why he doesn't want to listen to your advice, sorry this is the psychiatric nurse coming out in me, past traumas with fish, maybe his illness is affecting him to the degree that he is unable to rationalise other things.
Just a few thoughts. Take them as you please.
Good Luck
matt