I have a red fern macro that I think is thriving- the two fronds that I ordered have grown substantially and a third frond has appeared as well. However, the middle of the stem on the biggest frond is brownish/greenish. My cerith snails are regular visitors to this plant so I don’t think it’s algae—and the tip has continued to grow even after the discoloration happened. Any ideas? Sorry for the slightly blurry pic- taken from directly above.