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Fish/Black fin sharks


Hello I came home to fine one of my two black fin sharks dead, it was stuck to the filter but he wasn't small enough to be sucked by it (not cause of death) on looking at the shark when I took it out it appeared to have red blood like lines on its top and back fin, I have a 120litre tank set at 25 degrees 10% water change once a week with water conditioner and stress solution put in. I have had the 2 black fin sharks for around 3 months and they have been very good with no problems they are among afew sword tails, neons and 2 clown plecos. I am devastated if you could help as to why it would be much appreciated.

Hi Gary

Could be a number of things, but it sounds like ammonia poisoning. You need to check your water parameters (ammonia/nitrate/nitrite/pH)

10% water changes a week is not sufficient. You need to do at least 25% water changes every week and make sure you siphon the gravel to remove waste. Waste in the gravel will also cause an ammonia spike. Also replace the carbon in your filter once a month.

Raise your temp to 26 C (78-79 F)

Hope this helps, good luck!



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Richard Hight


I own and maintain several freshwater aquariums from 2 to 180 gallon. I can answer most questions about freshwater aquariums, including setup, cycling, maintenance, compatible tank mates, feeding. Moving? I've moved fish both across town and across the country and can help you get your little aquatic friends to their new home safely. I know and have experience with most freshwater community fish, South American Cichlids and African Cichlids. I don't answer questions about Goldfish or keeping Goldfish with Tropical Fish. I also don't answer questions about keeping crustaceans (shrimp, snails, crabs etc) with Tropical Fish, nor questions about saltwater fish or aquariums. I'm not available to answer questions on weekends, this is when I do maintenance on my own tanks.


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