Staurogyne Help

Hey all, new member here.

So I have a 20g that's been running for almost 2 years. Recently I realized that it'd been about a year since I fertilized with root tabs. Just got away from me somehow. I use Seachem Flourish tabs, which I break into pieces and place around (except for my swords which each get a full tab.) About a week after adding, my staurogyne repens started melting. They've been fairly happy and have very healthy root systems. The melt has been mostly the older, lower leaves, but a few of the stems came off too. It's not all of them. Pics attached of one post-melt and one currently melting.

My assumption, given these are older leaves and I just fertilized, is that the plants went "oh hey, I finally have good nutrients to work with, it's safe to drop these old leaves and start new stalks." It does appear that they are growing new shoots. I'm just curious if this is normal or if it's something I should worry about. My other plants (swords, cryptocorne, and valisneria) are just fine and very happy that I fertilized. Cryptocorne are also dropping old leaves but they do this on the regular and are crazy growers so I'm not worried about them. My staurogyne have never done this.

Tank is 20g long. Substrate is pool filter sand. Lighting is Beamswork FSPEC LED, 8 hrs a day. I don't have CO2 injection but I do dose with API liquid CO2 daily. Fish are tetras (neon and glowlight), cory cats and some nerites.

 

I do have the Flourish liquid fert, and I used to use it, but my tank is conventionally overstocked so it was giving me water quality issues. But, now my plants have grown in to the point that they're keeping the water crystal clear, so I'll try adding it again.