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Fish/adaptability of moving fish from 1 tank to another ( same water supply).


Hi Rich: My son inherited a 20 gal. tank 6 months ago. In the fresh-water environment, He placed a lemon Oscar, a striped, then tiger Oscar-all young. Within a month all 3 Oscars died. His tank was not quite crystal clear. I have a 5 gal. freshwater tank which I've maintained quite awhile & is crystal clear. One morning, Feeling sorry, I transferred 2 of my danios (a beautiful stripe-purple & striped yellow, both healthy  and energetic into my son's 20 gal. tank! Both tanks are in my house and use same water supply & declorinator. I placed  the 2 danios into his tank early in the morning to observe their behaviors throughout the day & to see any telltale dangers of stress/ill health. Throughout the next 2 days, everything appeared fine. The 3rd  morning my yellow danios was found floating (died). Of course I retransferred my purple danio back to his original environment (my tank) & felt very guilty and sorry re initial transfer.  
Rich: what probable/possible factors caused this danio's demise just overnight?  

Hi Ken

It is difficult to tell what may be wrong with the 20 gallon, other than it may have had disease in it from the previous owner. When you get a used tank, never use the same substrate or filter. It is best to start over with all new equipment and decor in a used tank.

It could also have a high ammonia content in it from the Oscars. Oscars are very messy fish and 3 of them in a 20 gallon could've polluted the tank beyond what the filter and bacteria could extract. Test the water or take it to your local pet store and they will test it free. I think the best thing to do is a 100% water change and new filter as mentioned above and recycle the tank.

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.


Many years of personal experience with fish and aquariums

HSG 2010-2011 prof

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