50% every two weeks is your problem, and sadly, there is no "probably" about it. If you do not have more time than that to devote to changing your water and doing proper tank maintenance, then this is not the setup for you, and you should get rid of your small tank right now. Your fish will continue to die and your algae problem will continue to get worse.
In order to make this setup work, you should be doing at least one 50% and one 100% water change per week. The tank is small and it is not cycled, so you really cannot get away with only doing partial water changes, especially so infrequently. If you think about it, if you do a 50% change today and a 50% change tomorrow, it adds up to 100, but it does not mean you've changed 100% of the water. Inevitably, there is some of the old water left, plus whatever the fish has added to it in that time, so over time partial changes become less and less effective at controlling ammonia. Also consider that you have to regularly clean the gravel to remove feces, uneaten food, and ammonia residue that are contributing to your ammonia problems.
If you want a setup where you only have to do 50% changes every two weeks, you need to look into getting a tank that is at least 5 gallons in size, filtered, and stuffed with live plants.
If you are having issues scheduling your lighting, I recommend an outlet timer. I use timers on all my tanks so that I don't have to worry about turning things on and off if I decide to go out that night or if I leave town for a couple of days. It's great not having to worry about it. Plus, they're only about $3 at the hardware store.