Nice to see a few planted tank people commenting, because I could use some feedback/suggestions on an algae problem I'm fighting. Apologies for the lengthy post.
I've been keeping a 20 gallon tank with my 4th grader for a couple years with neon tetras, cory catfish, some snails and marimo moss balls in it. This summer we got interested in live plants and added an anubias nana and vallisneria in early September. The val was spreading slowly and the anubias leaves started turning light green with dark veins, so in the beginning of October I started lightly adding Flourish and added a decent light. Throughout all of this the nitrates were increasing steadily, 10->20->30->40 ppm in subsequent weeks with 25% water change. So I started more frequent changes to keep the nitrates steady.
At the end of October we were going out of town for 2 weeks. To make sure the nitrates wouldn't get out of control, I did a series of changes the week before to get them around 10 ppm before we left. I also setup an automatic feeder and reduced the food (we were probably feeding too much anyway) and had the light on a timer 10 hours per day. When we left, we had a bit of brown algae that I was waiting for the snails to attack, but nothing else really. When we got back home Nov 8th the tank was pretty well covered in algae. Brown algae on the plants, a carpet of green algae on the glass and black beard algae on the filter, driftwood and fake plants. It looked pretty gross when we walked in. I tested the nitrates and then were still right around 10 ppm after two weeks.
After thinking on it, I can only think of a couple things that changed while we were gone. 1) I wasn't adding Flourish those 2 week and 2) I had reduced the food. Would it make sense that this created a "nutrient deficient" environment that allowed the algae the pop up? Would algae have stayed dormant when the tank had lots of nitrates, only to attack once the nitrates were lower? That doesn't completely make sense to me, but it's my best guess at this point.
So, here's my plan of attack so far:
I removed and bleached all the rocks, driftwood, artificial plants, filter (just the intake tube) and the anubias to get rid of the black beard algae
The things I couldn't remove, I spot treated with hydrogen peroxide while the filter wasn't running
I scraped most of the green algae off the glass (I read later that it may be better to let it mature for 3-4 weeks and then manually wipe it out so it doesn't release new algae spores in the water)
I restarted my regular weekly water changes and light Flourish dosing
I added a few otocinclus catfish to attack the algae (they've already gone to town on the brown algae)
I'm going to monitor for a couple weeks; If things aren't trending in the right direction I'll try cutting the light back to 8 hours a day
I also thought about adding some kind of floating plant to block some light, but don't want to introduce too many variables
Anything else I should be trying to get this under control and balanced out? Any other theories on what might have caused things to go haywire so quickly?