Hornwort going down hill

I'm no expert (I'm pretty darned new actually) - but as nobody has answered, let me try:

How often do you change your water? Do you add anything to your water?

My guess is that your hornwort has used up the nutrients in your water. I have some hornwort and the stuff grows so quick I think it has to be a nutrient sponge!! From what I've read, you'll want to do a large water change (40-50%) once a week, and adding the proper nutrients to your water will help quite a bit.

I'm not adding nutrients yet (that starts this week), but I've noticed that my hornwort starts to look brown around 5 days after my last water change, but after a water change it gets more green.

Any real experts want to back me up? (Or correct me)

hornwort

hornwort is an algae, so if you use any algaecide it'll suffery way more than the other plants. Hornwort is also very sensitive to copper, rid ich will bother it.

Of course it also likes LOTS of light and not too warm temps.