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Most of us have heard tales about how sea cucumbers can “nuke” your tank. However most of us have only heard this by 3rd parties. Unfortunately I myself have experienced it. I had a black sea cucumber, about 4-5 inches long, but could stretch to about 7 or 8 when he wanted. The last few weeks of his life he started to climb into the rocks, not acting like a normal sand eating cucumber. Late on a Friday night, my cucumber was in a rock, with his mouth tentacles out in the water, acting very strangely. I decided I would help him out of the rock. I had done this on multiple occasions as I am the obsessive mother reefer type who does whatever she can to help her critters. If you have ever held a sea cucumber, you will know that they are very smooth and slimy, not easy to grasp whatsoever. So trying to get this sea cucumber out of the rock was proving difficult. I was able to push him out one side after almost 10 minutes of struggling. He had a few abrasions, but this also had happened before and he healed just fine. So I put him on the sand and called it a night. I was going to stay the night at my Dad’s house, which is about 15 minutes away from my Mom’s house. On the way, I was watching the web cam I have set up for my tank. I noticed that my copperband butterfly was out swimming! It was already after 1am, all the lights were off, and no reason for her to be out. But she was silly, so I let it slide. A few minutes later I noticed my 2 clownfish were also out swimming! This was very strange as they live in their anemone. I then also saw my blenny darting about. This all added up in my head that something was wrong and I needed to go back and figure out what was wrong. When I arrived back at my Mom’s house I was able to see what was happening. All the fish were breathing heavy to the point of hyperventilating. So I sprang into action. I knew in the back of my head about the sea cucumber toxins. I pulled the cucumber out, who was very limp and lifeless and put him in a cup of tank water. I started up 4 different air stones/air pumps to increase the oxygen. I had 20g of RODI already beginning to heat up as I do water changes on the weekend, so I threw in the salt so it could begin to mix. I got out all the carbon I had, 6 pre-packaged bags, 100 grams each and rinsed them and put them in the sump baffles. I also increased the skimmer production. Waiting for the water to be ready was hard. I was also struck with the choice of doing a water change, ~20% on a ~100g system or put the freshly mixed water into the quarantine tank and try and get the fish in there. My Dad and I decided to do the water change. The quarantine tank was still being cleaned after being used a few weeks before and would need to be emptied, finish cleaning equipment and filled. And then try and catch all the fish! So we did the 20 gallon water change in the display. I had 9 fish in the tank. 2 clown fish, 2 dragonface pipefish, 1 fancy gumdrop coral croucher, 1 randall’s goby, 1 copperband butterfly, 1 tribal blenny and 1 mandarin. The butterfly and the blenny were doing the worst, followed by the clownfish. The other 5 fish seemed to be either not affected or only mildly affected. After 2 hours of doing everything I could, I had to go to sleep as I had prior commitments the next day, and there was nothing else I could do. At this point I also noticed the cucumber was actually still alive. I wasn’t up to making any decisions about him so I put the cup he was in in the sump so he would at least stay warm. I turned off 2 of the air stones and left 2 of them on. I checked on the camera when I woke up and noticed I did not see the butterfly swimming and thought I saw her body on the sand, which was expected. Everything else looked “okay”. So I went to my Mom’s house and sure enough, the butterfly was dead and I removed her body. All the fish except the blenny looked pretty good. The clowns were still breathing a little heavy, but nothing compared to just a few hours before. The blenny though was very obviously in distress. I started mixing 15 gallons of water so I could do another water change later on. When I got back from my day, the blenny was dead. This was very upsetting as he was my 3rd fish and I had had him for over a year. At this point all the other fish were fine, although a bit confused about the 2 fish losses. The cucumber was still alive, but barely. So I put him in the freezer so he could die quicker as there was no reason for him to suffer. I also performed the 15 gallon water change and left the 2 air stones going, just to be safe. Later on that night I removed the air stones. During all of this I did add about 8 oz of StartSmart, a bacteria to help the nitrifying process (however I do not think this played much of a part, but for documentation sake I included that here). It has now been 7 days since the incident. I have removed the carbon. All 7 fish look great and seem fine. I can only thank being prepared for such situations for the small amount of fish loss, and also being so quick about it. Sea cucumbers are not evil and not a guarantee they will “nuke” your tank. Only severely stressed cucumbers release their toxins. So if you have a cucumber or are planning to get one please keep this in mind. 1. Don’t bother the cucumber. Some cucumbers are just weird, keep an eye on them, but don’t bother them. Get to know his or her behaviors and antics 2. Have plenty of RODI water on hand; enough to do at least 20% water change, more if possible. 3. Carbon, carbon and more carbon. 4. Don’t stock any fish or inverts that may disturb the cucumber. 5. Realize that it is a risk having them in the tank. Cucumbers are wonderful creatures and can be big helps in the home aquarium with the sand bed. Despite what happened, I miss my cucumber and wish he had managed to live. I caused his stress so I do not blame him. I hope my experience will help others in case they too encounter this problem or at least educate others about this issue. If you have a cucumber and he releases his toxins, please try and document what you did or do, as I believe more information on this matter is needed. However I am not willing to stress a cucumber out enough to release his toxins and see how it affects the fish and what other methods could be implemented to combat the toxins (please do not do this just for research!!). Thank you for reading, good luck, hope for the best, plan for the worst and happy reefing!