Try doing a mind/ body relaxation exercise. Get comfortable, close your eyes and imagine your entire body is filled with little light bulbs and starting at your toes start imagining these light bulbs dimming and slowly going out continue doing this through your feet and up your legs, all the while allow your muscles to relax, don't rush it and continue to take deep relaxing breaths, you should start to feel your muscles wanting to relax before you even get to them, ignore the heart and lung area but continue switching out the lights in your fingers and hands, bet you can't actually make it too your brain before your asleep.
If that doesn't work try imagining that you are on a beautiful tropical beach lazing in the warm sun and can hear the gentle rymthic swish of gentle waves washing on the beach.
And if all else fails my husband is GAURENTEED to fall asleep "watching" car racing. Well he says he was watching it but the loud snores escaping him prove him wrong
And even though it sounds hokey a glass of warm milk does make you drowsy, the heating of the milk (but not actually boiling it) changes the chemical composition and helps your body release "relax" hormones.
Just a wayward thought....since you have fish and watching fish swimming, birds flying and or patting a cat or dog are all suposed to relax and reduce heart beats try just staring at your fish for a while before going to bed. Just watch them in a semi detached mode rather than worrying about their food, cleaning the tank, rearranging it or any of the other activities surrounding keeping fish, just watch them in a peaceful state of mind and see how that goes.
Good ZZZZZZZZZZZZZZZZZZZZZZZZZZZZ