[jbherpin]

If I were the OP, I would look to follow Ed's advice... From the pics, there seemed to be a lot of organics underwater, and this will just encourage the flatworms. As stated, although not considered parasitic, they are proven to cause stress. I would both remove the existing worms, and consider removing some organics(maybe even a spongefilter to correct stagnation and biodeposits, etc.).

JBear