What are the temps in the tank? They prefer cooler water, but if you can't lower the temp because of other fish you will have to add extra aeration to the tank to provide the needed oxygen content for them.
It looks like it is in a blackwater tank, and you likely don't get much for green algae growing you'll have to see if it takes to a high quality algae wafer or better yet the repashy gel food for vegetarians.
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