Well the mistreatment of fish is nothing new and, unfortunately, its prevalent among the fish-keeping hobby. Many are unwilling to change what is "working" so we can only offer suggestions and answer their questions the best we can.
Dylanfish, basically, the answer to your algae problem is as follows:
You have algae because your water is high in nitrates and probably phosphates from fish waste, and/or leftover food. To solve the algae problem you have a variety of solutions.
1) move the fish to seperate tanks
2) increase your water change schedule, and increase the bio filtration on your filter
3) start planting live plants to help consume the high nutrient content of your water.
A marimo ball is algae, it is NOT an all-powerful plant that will replace an algae eater.
Floating plants such as duckweed, frogbit have an advantage and will consume your nitrates very fast, you can take out the xtras and toss them when they get too big.
Hardy plants that attach to things are effective, these are java ferns, java moss, and similar plants.
A combination of 2 and 3 will be most effective in keeping your algae levels down. However, option 1 will be more effective in the long run and cost you less time had work. It will also help with your fish's aggression.
I hope this answers your question.