I seem to have a lot of flat worms on one particular bunch of mushrooms. Are they harmless and can I get rid of them as they do look unsightly. My tank is a RSM 130 with live rock and coral (pulse, bubble, goniopora, finger and cabbage) tanksmates are 2 Common clowns, 1 Yellow Tang, 1 Coral beauty and several hermit crabs and snails. Any advice gladly recieved.
Thanks for your letter, and as to flat worm problems, it depends on their numbers if its really a problem or just a happening that will pass.
Keep in mind these worms are photosynthetic, as they are attracted to light. Placing a lamp near the aquarium at nighttime will attract them in huge numbers making it easy to siphon out the majority of them very early the next morning. The reduced number may give other biological control methods a better chance at bringing their numbers under control.
As for biological controls, the Banded Goby, Amblygobius phalaena, is said to eat this flatworm. Also, Wrasses, e.g., the Sixline Wrasse Pseudocheilinus hexataenia, Leopard Wrasse (Macropharyngodon meleagris), and Yellow Wrasse Halichoeres chrysus. Also some Anthias are thought to be an efficient consumer of this pest, as are Peppermint Shrimp (Lysmata wurdemanni) and also those in the Lysmata species. In fact, the Mandarin fish (Synchiropus splendidus) has cleared up the problem in some of my past reef systems. As had some pipefish. Also, the Sea Slug/Nudibranchs in the genus 'Chelidonura' are believed to be a very good consumer, although very short-lived slugs. Also, scooter blennies and hawkfishes may also consume them.
There is also some thought these flat worms can rapidly go away due to some biological clock, lack of foodstuffs or a biological competitor. Also, there's some thought the over use of iodine supplements, which flat worms may concentrate in their internal fluids, may lend itself to promoting their proliferation.
There is some thought that killing these flat worms, such as Convolutriloba retrogemma species in large numbers could present a toxic condition in the closed system by stripping its oxygen in the degradation of large numbers of these pest flat worms and in the release of iodine in some format, as they harbor iodine in their tissues. Increased water flow and improved protein skimming is also helpful if you plan on using any products to kill them. But I don't recommend such approaches.
Hope this helps,