Terrible Advice Tuesday: Sexist Flatworm Removal

Terrible Advice Tuesdays: If you have a red planaria (a type of flatworm) problem, add a mandarin to your tank. The trick though is to add a female mandarin as they go after the flatworms more aggressively than males.

The rest of the story: This terrible advice has two parts, so let’s break it down:

Part 1:  A mandarin will eat flatworms. I’ve come across some circumstantial evidence that mandarins will eat flatworms. The key word here is “some”. For every person who says their mandarin eats flatworms, there was easily 3 or more people who said their mandarin doesn’t touch them. Here’s the really terrible part of this advice: you won’t know if the mandarin will eat flatworms until you add it to your tank. If it does it flatworms, once the flatworm population is gone, then what? Maybe, maybe,  the mandarin will switch to eating frozen food. I’ll assert that a mandarin suddenly making a switch to frozen food is twenty times less likely than a mandarin eating flatworms. If the mandarin doesn’t spontaneously switch to frozen food then you’re left bombing your tank with pods to try to keep the mandarin alive. And no, the small refugium that is part of your sump won’t produce enough pods to keep the mandarin alive.

Also, once the flatworms are gone, you’re not going to go dump more flatworms into the tank to feed the fish! The whole reason for getting the mandarin in the first place was to remove the flatworms!

Part 2: Female mandarins will more aggressively eat flatworms than male mandarins. This part of the advice sounds like circumstantial evidence taken to an extreme. Some hobbyist likely had a pair of mandarins and the female happened to eat flatworms while the male didn’t. The conclusion? Having a female mandarin is the key.

If you have a red planaria problem, I recommend an arrow crab or a Hoeven’s wrasse (Halichoeres melanurus). Yes, both of these animals may, or may not eat flatworms. If they don’t, the arrow crab can easily be removed and the Hoeven’s wrasse will eat frozen food very easily. Disclaimer: Hoeven’s wrasses sometimes eat clean up crew members such as shrimp and crabs. I’d rather have you lose your clean up crew than take a risk on a mandarin eating flatworms.

Finally, I’m not a fan of medicating your tank to remove flatworms. These medications will likely kill the flatworms and when the flatworms die, they can release toxins that can poison your tank.

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Comments for this article (8)

  • Cindy says:

    Thanks for this correction. I was wondering what your advice would be on bristleworms in my tank. I have to tell you it freaked me out when I saw them…they are about 2-3inches long and appear to be several…ugh, Thanks for any advice you can give me, as you tube didn’t help, I made the traps shown in their videos with no success


  • Melody says:

    I also would like information on brissle worms. I know a few are fine. But I’ve got more than a few. I know my husband over feeds and am working on that. But what more can I do. Also any info on berghi nudibranch for aptasia are they reliable?

  • Kyle O says:

    For what it is worth……..I have been at this for a lot of years now. I find Mark’s advice to be spot on.

    Regarding bristle worms, that is a very different problem than flatworms. Bristle worms are part of an effective clean up crew. If you have too many, you are over feeding your tank.

    Regarding Aptasias………….I had a problem that went from bad to worse. One day my daughter started counting (she is 10) and I made her stop when she got up past two hundred. I picked up a Mated Filefish on the advice of a friend……..and now I have a difficult time finding any Aptasias. I see a few small ones in between rocks where the Filefish obviously cannot reach.

    Needless to say I am thrilled……..but I am now waiting to see if the Filefish will switch to some other food source and/or starts picking on coral polyps, which will present a different set of problems similar to what Mark is addressing in this episode of TAT.

  • John says:

    Try Bicolor Pseudochromis and some other Dottybacks(not all Dottys will work) for the brissles. Coralbanded shrimps work too.

  • Frank says:

    I had a bad flatworm problem in my 180g. I added a female spotted mandarin and a melanurus wrasse with no results. I triple dosed flatworm exit 3 times within a week ($200) (shut off skimmer) and only killed about 90 – 95 %. They came back. Strangely enough I introduced a velvet nudibranch only to help control the flatworms and I haven’t seen any in the main tank in several months. I see the odd few in my overflows but they have not spread to the display since. Sadly the nudi disappeared before I could pass him on.

  • Julie says:

    I also had a flat worm problem in my 180. I tried the spotted mandarin, Melanrus wrasse and a few velvet nudibrach’s to no avail. The Nudibrachs did eat some of the flat worms but they disappeared or got caught on the filters of my vortechs. I did not want to waste any more money or see any more nudibrachs die so I suctioned out as many flat worms as I could, changed the flow, cut down on my feeding and over time they declined in numbers. I did notice recently some flatworms in my sump but none in my display tank. As long as they stay in the sump in limited numbers I am good with it.

  • Vince says:

    I have used velvet Flatworms for years. They will gobble up flatworms like it’s their favorite food. It’s fun to watch them do it too! Mine like to take trips to my sump at times, however. Just be sure you keep pumps covered so they don’t get sucked in!

    Hope this helps,


  • John says:

    I have a male mandarin which has cleared 2 of my tanks of flatworm. It also eats frozen brine. I have never seen him eat a single flatworm and was told by my lfs its because they eat the eggs and young. My mandarin is not clearing my third tank. But as pointed out previously . . Animals are far from predictable.

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