Simple question, difficult answer.
Cleaning is the problem. Old tank syndrome. Nitrates and/or phosphates thru the roof.
Even feeding four days a week, if you are feeding a lot during the feeding period, a bunch may not get eaten and fall into the substrate and rot, then turning into ammonia, then nitrite, then nitrate.
Got a nitrate test kit? Get a reading and post it. If it is over 20-25 ppm, there is your problem.
To fix the issue, you have to start doing regular, weekly water changes. That is the only way to get rid of the algae. You can't just start willy nilly though if you haven't been doing them much.
Start with a 5% tank volumn once a week. Then increase to 5% 2x/week. Then 10% once a week, then 10% 2x/week, then 20% once a week, so on, until you get up to 50% a week.
Each water change, do a deep gravel vac on at least a portion of the gravel. In the beginning this is going to be hard because the water changes are going to be so small. But if you do bigger than 5-10% to start, you will shock the fish and they will die.
Once you get up to 50% a week, you have to do that from then on, at least every other week.
Hard facts: If you aren't doing at least 10% a week, or 25% every other week, the nitrates in the tank are slowly poisoning the fish. Kind of like if you have lead paint in your house. They don't show signs right away....it takes time. But eventually, it starts to show. And it takes a long time for them to die a long painful death.
Or you can look at it another way. It would be like you and your friends and family living in a nicely sized apartment building, with an endless food supply, with no doors or windows, and no toilets. After a while, it will smell pretty nice in there, eh? A month wouldn't be too bad. Imagine 3 months. A year.
Hate to put it that way. We like to forget that our fish are more than just decorations that move, but they are pets that are responsibilities. If we think they don't have feelings, buy a king tiger pleco and pull it out of the water. They croak from the suffocation. Drop a goldfish in water that is too hot or too cold and watch them freak out from the pain. They definitely feel. It isn't pleasant to watch them die.
Back to the algae. Yeah, start putting the python to use. The algae will go away pretty fast if you do water changes. Get the poop out and the excess food, and you'll be amazed.
P.S. There is no such thing as a fish that eats poop. Plecos and other bottom feeders don't. It is a myth. And if you don't want to do regular water changes, find a friend to take the tank and fish. They really deserve someone who will not slowly poison them to death. I am not trying to be mean, it is just the facts, mate.