Why do this keep coming back

That looks just like Brown Diatoms which is common for a ton of reasons. Try reading this article and it should guide you on the fix and resolution on it.

Brown Diatoms

votavk said:

I keep getting this algae coming back, but not sure why. I’ve wiped the glass down a few times and it keeps coming back which is confusing.

I hope that you later read the article that was suggested to you? I used the instructions in it for my own tank and it was very effective in taking care of them.

That definitely looks like Brown Diatoms, I remember getting this a lot in my tanks and I got super frustrated by it as I would clean it and it would just keep coming back. I ended up looking into it and that was when I found out what it was. I would definitely read the article suggested to you above as that will be a great help at you getting rid and keeping it at bay.