All those in the fish hobby know all too well about algae. No matter what you do with your tank, inevitably you will get algae. It's completely normal and mostly because everyone wants to see their damn fishies! So your tank either comes with a cover and a bulb installed or you get like I do, a strip light that goes over the top, and in this manner I offer RGB lights and can also control the brightness, and put it on a on/off schedule.
It usually starts on the glass, as mine did. *There are tons of different algaes and why and what they look like. Mine is just your typical green algae.
So I was forever cleaning my glass, and I noticed the back panel of glass building up. Then BOOM, it was on both sides and a slow build-up on the gravel in the rear corners. Then a few weeks later it got about as bad as you see below, or maybe worse. And all of those little white looking seed things? damn snail eggs!! And they are on the glass if you see them.
I added a 2nd filter for better water turnover and better ability to clean. But MUCH better - and I never used one before and didn't know what to think. It's a UV filter called the "green killing machine" - just a little tiny filter that doesn't take in a lot of water in at a time. But internally it's got a UV bulb that all the water passed by, and it cleans it quite well. And better, it started cleaning it in more than the water, it took it from everywhere and did a fantastic job for $50, IMO!!! 4 days to get here and I have more to go, but getting there!