What is this? Some kind of algae??

So I'm still cycling the 75 gal tank. I think I left the lights on too much over the 4 day weekend and started to develop a blue-green colored algae on the sand. I've reduced the amount of time the lights are on and it seems to be helping.

But now I'm noticing this purplish fuzzy type stuff on one of my plants. It's at the tips of nearly every leaf. I'm not sure if it's part of the plant or if it's an algae growing on the plant. The plant is Heudelotii.

I'll try to get pics, although I'm not sure how they will turn out. I'm just curious if anyone else has heard of an algae that is purple and fuzzy before...

Will excel harm any of my plants? It's a low-light, low-tech setup - dwarf sag, java moss, java fern, hornwort, anacharis (which is about dead - apparently I can't do that one...), etc.

Here are a few pics. It looks more red in the pictures than when I'm looking at the tank. It's more of a fuscia color in real life...

Well geez. One algae (the black one - assuming of course that this is what i have...) says not to do water changes to help get rid of it (I haven't done any water changes on this setup yet - just been dosing ammonia when the ammonia level drops - trying to get it cycled). The other says to do a 50% water change and blackout to help get rid of it. So which do I do??

Also - how long can I keep the tank lights out before the plants start to suffer?

I'd really like to avoid battling this with chemicals if at all possible...