I’m sorry to hear about your ongoing troubles with flatworms. But if the flatworms have become so numerous that they are problematic, and controlling them biologically with blue velvet nudibranchs has not been successful, then the Flatworm Exit is probably your best alternative. I know you are concerned about the effect the toxins released from the dead flatworms could have on your seahorses, so this is what I would recommend, Julie:
(1) First obtain some fresh activated carbon and a Polyfilter Pad (from Poly-Bio Marine) that you can add to the external filter for your seahorse tank after you have treated with the Flatworm Exit. The activated carbon and Polyfilter Pad will remove any toxins or contaminants from the aquarium water following the treatment, so the seahorses won’t be affected.
(2) Remove the seahorses and any other delicate specimens such as cleaner shrimp or starfish to your hospital tank before you treat the main tank with the Flatworm Exit. If you do not have a hospital tank or quarantine tank set up, a clean 5-gallon plastic bucket (new and unused, NOT an old scrub bucket!) can serve as a makeshift hospital tank. It should be aerated and equipped with hitching posts and perhaps a heater, but nothing else. That will make it safe home for the seahorses and other sensitive specimens temporarily while you treat the main tank with the Flatworm Exit.
(3) Siphon out as many of the flatworms from the glass and other areas of the aquarium as possible, just as you have been doing so diligently all along, Julie, and then administer the Flatworm Exit to your main tank according to the instructions.
(4) After the Flatworm Exit has done its job and destroyed the flatworms, perform a major water change on your main tank and then install the fresh activated carbon and the Polyfilter Pad that you obtained previously in the hang-on-the-back filter or canister filter on your seahorse tank so they can remove any remaining toxins or contaminants.
(5) Filter the water in your main tank through the activated carbon and Polyfilter Pad for 24 hours to remove any residual harmful substances from the aquarium water, and then test all your water quality parameters (ammonia, nitrite, nitrate, pH, and salinity or specific gravity) to make sure the readings are as they should be.
(6) If everything tests out properly, as it should, go ahead and return the seahorses from the hospital tank to your main tank, but make sure you have some additional freshly mixed saltwater ready to go in case another water change seems advisable.
Following these steps should allow you to treat your seahorse tank with the Flatworm Exit and destroy the flatworms without any danger to your seahorses, Julie. But before you do anything else, please read through the following information, which is what I normally advise seahorse keepers regarding flatworms:
Flatworms and Seahorses
There are a few parasitic flatworms that plague seahorses, such as tapeworms (Cestodes) and blood-sucking flukes or trematodes, which are like tiny leeches, but these require a host to survive. Most of these flatworms that find their way into our aquariums are free-living (nonparasitic), and the vast majority of these are benign, harmless creatures that are often best ignored, although they can be troublesome when their population gets out of control. If you have the noxious kind of flatworms, or a population explosion and they are crawling on your seahorses and causing irritation, they should be eliminated, but by and large flatworms are more of a danger to live corals/clams and the reef keeper than a danger to seahorses. They can actually cause more harm when they are dead than when they are alive, because their decaying bodies can release toxic substances in the water when they die en masse.
The first step in eliminating the flatworms is to siphon out as many of them as possible so that the remainder can be eradicated safely. One possibility is to use a blue velvet nudibranch to limit the flatworm population naturally as a means of biological control. That species feeds naturally on flatworms of the type that often appear in reef tanks.
If you can possibly obtain a blue velvet nudibranch, there would be no harm in putting it in your seahorse tank in order to see if will feed on your particular flatworms and eliminate them naturally. That would be preferable to eradicating them chemically, which is the other alternative we will discuss at the end of this letter. But it can be difficult to obtain a blue velvet nudibranch, or if you are able to get one, it may not feed on the particular type of flatworms that are in your tank. That would certainly be worth a try, though…
In the meantime, here is a link to a good article on flatworms by Bob Fenner, which is loaded with good information and a number of pictures, and may help you to determine if your flatworms might present a risk to your seahorses:
Click here: Flatworms
If you want to be absolutely safe, you can certainly eradicate the flatworms from your tank. Flatworms are more of a risk to reef keepers because some species attack clams and certain types of corals, and reefers swear by a product made by Salifert called Flatworm Exit. It wipes out flatworms but is said to be completely harmless to other invertebrates and fish when used as directed:
Flatworm eXit itself is quite safe to fish and invertebrates. However, the body fluids of flatworms can be toxic to some reef inhabitants when present in a too high concentration. This body fluid is sometimes excreted when flatworms die. When you use this product it is important to do the following first:
*Siphon out as many flatworms as possible.
*Keep sufficient fresh activated carbon in a canister ready.
*Turn off UV, ozone and remove activated carbon before treating the tank.
*Keep the skimmer turned on.
The following remarks are meant to reduce the amount of the flatworm’s toxic body fluids in the water.
Many people have treated their reef tank(s) successfully using Flatworm eXit without any problems. The most important factors are reducing the number of flatworms before commencing with the treatment and reducing the amount of the flatworm’s body fluids, released when they die, as fast as possible.
Do not underestimate the number of flatworms in your system. In a few cases a significant number of flatworms can be hiding in for example crevices. Blow in such and any other potential hiding places water to blow any flatworm out of there. For that purpose you can use a powerhead or a turkey baster. Siphon out those flatworms as well.
Do not underestimate the amount of toxic body fluids these flatworms can excrete. This can be reduced significantly by really siphoning out the flatworms before commencing with the treatment. Further significant reduction is accomplished by siphoning out as many dead flatworms as you can. Any body fluids released by the dead flatworms in the water has to be reduced further by using about 1 pound of fresh high quality carbon for every 50 gallons. The carbon has to be used in a canister with a sufficient forced water flow.
Take sufficient time for treating the tank. That is, do not treat your tank in a hurry. Also take time to monitor your tank for at least 6 hours after the treatment. It is also wise to have at least 25% water ready for a water change if required.
Flatworm Exit is available online from a number of different sources. I have never used this particular product, so I cannot vouch for it or say for certain that it’s safe with seahorses, but if it’s used in reef tanks and doesn’t harm the delicate corals and invertebrates, it’s very unlikely it could be harmful to seahorses when used as directed. And if you remove the seahorses while the main tank is being treated, and then filter the aquarium water through fresh activated carbon and a Polyfilter Pad afterwards, there would be no danger to your ponies…
If you find the flatworms unsightly, or feel they may present a health risk to your seahorses, go ahead and eliminate them. Just observe the safety precautions outlined above.
Best of luck getting rid of your flatworms, Julie! They most likely found their way into your aquarium has hitchhikers on a piece of live rock or live coral, or perhaps amidst some macroalgae.