Plants dying?

So I've had my betta fish tank for about a month and a half now (betta only added about 2 weeks ago after tank finally cycled). As the title suggests, I'm noticing that my aquatic plants are slowing turning brown. I did my best to check online for light requirement before buying, but I can't remember all the plants specific names. I have them in Activ-Flora substrate so I assumed they would be good to go for a while at least. I have florish and excel, but I was worried about adding them to the tank and messing up the water conditions. I have another tank (shrimp only) that I almost never touch and those plants are growing like crazy, but it's a different substrate. Any advice is welcome, but please be kind if I'm being dumb 😅