Carib Sea Aquatics Rhyzomat Subsurface Root Mat, 12" x 24"

First time my plants stayed planted in my African Chiclid tank!

So I added a rhyzomat to my aquarium to help with the plants, and I did cover it with gravel, but there were a few strands sticking up... originally I did not think this was a problem, but after a couple of weeks something started growing... at first it was a few globs that looked like moss, and then it started to look more like a black algae, I was suctioning the gravel and trying to get as much out as I could... that went on for a couple of weeks... about three days ago I vacuumed out all that I could see and did a 25% water change. The next day it was back, so I vacuumed it again, and did a 25% water change. Today I was busy and had not time to look at it until later in the evening, and I found what looks like moss balls or algae balls growing in clumps on the bottom of the tank (see pictures). Yes that happened in less than 48 hours, and I have no idea what to do... I don’t know what it is and I don’t know if this is going to kill my fish... what I do know is that my plants look like they are being taken over by a mossy blob, it grows faster with water changes, and I think I am going to have to get a new substrate... I’m not happy... and I will probably puke while trying to clean this out. 🤦🏻‍♀️

Plants are growing!