Bacopa plant stem rotting

[Alec]

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I keep having issues with stem plants rotting off at the bottom. In the image below you can see what I'm talking about. The stem gets real stringy until if breaks off. On my bacopa plant, it has new growth up top, but the stem seems to be rotting. What is causing this? 

[xXInkedPhoenixX]

I have bacopa in my tank that was grown out of water, once submersed the growth changes and what was once above ground can drop off. Now that being said is this new Bacopa? What you can do is pull it, trim it, and replant it. I trim the tops of mine fairly frequently to popagate a bit more of a bushy look because it's not quite where I want it yet. It's a pretty resilient plant I'm finding and propogates well. Keep in mind I've only been growing Bacopa for a bit over 6 months. Others might have tips- there could be lighting or nutrient deficiency. I run low tech tanks with no heaters or fertilizers and it seems to do well with me.