Err... they're suppose to be one of the hardiest, easy to care for aquarium plants, yet I only have bunch left after buying 3.

I had them floating, and anchored to the side with a suction cup. Eventually they started to die and melted away from the anchor and became free floating. I left them like that, since they ended up settling where I wanted it anyway. After another week, two of the bunches were totally gone and I had to remove them.

I'm not left with 1 stem. I slightly buried it in the substrate, and it's been doing okay there for the last week or so, but it doesn't have any new growth. It's just kind of existing.

I have ultra-low light, but I manage to keep various other plants healthy and with ample new growth. Stuff like Hornwort, Water Sprite, Anubias and Sword plants do just fine, while this Anacharis seems to just die off.

Would there be any reason Anarcharis would die, but not any other plant?