I don't have a lot of experience with this, but I had a large dino outbreak a few months ago. I'm not saying that chemi-blue caused it, but it certainly made it worse. I've tried adding it back in a few times since then (if I remember correctly, it was chemi-blue elite) and every time dinos have come back. I since have installed a UV sterilizer, specifically the 9w Green Killing machine. While it's been running, the dinos have been kept at bay. My outbreak went away nearly overnight. My theory as someone who doesn't have a ton of experience (only have a 9 month 20g cube) is that chemi-clean works too well for smaller tanks. It causes near sterile water conditions that allow whatever dinos I have (which sound very similar to yours, not on the sand bed, long brown strings) to come back in earnest.
For me, just taking the chemi-blue out helped my outbreak, but what really killed it and has kept it at bay is UV sterlization