Am I Doing Something Wrong?

For starters, I have a 20 gal tall hex tank. It's been established since around January. Using the heater and filter ( 20) that came with it. In my tank I have 1 Buenos Aires tetra, 2 ornate tetras, and 2 white finned rosy tetras. I have two ,and rocks on the bottom. I do 20-50% water changes every Sunday depending on the amount of poop and other nastiness in the tank.

I've been battling brown algae for like 3 or 4 months now and I can't seem to get rid of it. I don't know if its because the food ( I use tetra min tropical flakes) sinks to the bottom really quick and my fish are lazy so they just let it fall then go and eat it, or if it's the poop, or if I'm just doing something wrong but it's everywhere. I changed the plants about 2 months ago and they are nasty now. I just can't seem to get rid of this .

I tried lights on, lights off, getting new plants, vacuuming the **** out of my gravel and I'm at a loss. Can my fish hang out for about an hour in just a bucket with no filter so I can give everything a thorough scrub and maybe change my gravel or will I have to get another tank cycled to do that? Is there anything relatively cheap that I can do (not getting more fish/animals) to get rid of this stuff or should I just keep waiting?

pictures attached! Thanks!

 

Welcome!
Tetras are schooling fish that require 6 or more of their own species. That's all I can see is wrong.

 

Your algae isn’t that bad IMO.

Add a nerite snail, see if that helps.

My tanks are crystal clear (luck, not skill). My “secret” is a mystery snail and a nerite snail in every tank. Even pest snails in a couple of the cleanest.

And frequent, large water changes.

And control your feeding.

My #1 solution is to add live plants. They will out compete the algae.

Your light adjustments were on track so I would play with that some more if you don’t add snails.

 

Welcome, I have heard 5 or more is recommended for schooling fish. Like Hunter1 said live plants with help with the algae

 

And control your feeding.

I think this is your issue, or at least one of them. With those fish, you shouldn’t be having any food left after about 30 seconds. If you put in enough that some is reaching the bottom, and they’re just lazily eating, you’re putting in too much, or too often.
Try feeding less, or less often (1x every other day), and see if that helps.
You’ll still need to resolve lighting also. Too little light is better than too much, for combatting algae.
And yes your fish would be fin in a bucket for an hour or two while you clean. Put the heater in with them, to keep temp stable, then add warm treated water to tank before returning fish so the tank is the correct temp too.