Mangrove help

[M&C]

I'm trying to figure out the cause of a small algae bloom in my tank. I haven't added much to the tank in the last few weeks except for 2 red mangroves, a peppermint shrimp, and a single head of a mushroom coral--not exactly what I would consider a huge addition to the bio-load.

 

I feel like it may be the mangroves but I am unsure. It's really hard to tell if they are doing ok or not. One mangrove has 2 leaves, and a single root coming out of the bottom. The other mangrove has no roots and no leaves. The stalk on this plant looks a tiny bit wrinkled, but it's hardly noticeable. Also, both stalks are an ugly brownish/black color below the water. Above the water line, both stalks remain green.

 

Does this sound normal for mangroves, or is it possible that they are dead/dying and releasing nutrients into my system? Any other plant with black/brown tissue sounds like a dead/dying plant to me, but the mangroves are still green above the water line, so I'm not sure what to think.