Well, shoot. A few weeks ago I trimmed some HC that had little clumps of what looks like black beard algae (BBA). Never encountered it before then. It's back and is in a couple different spots - on my rocks, on the HC, and on a tall plant's leaf. Also, some thin thread-like algae that might be "spirogyra" is forming over my HC.
I think this might be due to fluctuations in my CO≤ levels, since it's DIY and running straight into my canister filter. So I need to decide whether to...
A) Construct a PVC pipe CO≤ diffuser, like synaethetic suggested
Now that you are using a 2213, I would recommend constructing a PVC pipe c02 diffusor. They are cheap and easy to make with a trip your local hardware store.
B) Make the jump from DIY CO≤ to a paintball system or whatever (need to research this a bit, $ is the obvious factor here). Get a glass diffuser. ?
C) Start over! I want to de-rim my tank anyways. But then again there are a grip of baby shrimp under my HC carpet that probably wouldn't make the transfer. And I don't know how much of the HC I could transfer without transferring the thread algae stuff or the BBA also. If I did start over though, I think I would do 100% dirt capped with sand again. As much as I like the Eco-complete, and as much as the glosso seems to like it, the HC went nuts with the magic Idaho soil. ...the best potatoes do come from Idaho dirt...
Pictures of the algae to come...