I have a biorb 60ltr cold water tank with two fan tails and 3 neons for about 3 weeks there has been a bubbly oil like residue at the surface my fish are also losing their colour what can this be ?

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Thousands of years ago cats were worshiped as gods...cats have not forgot this !!!!

OK, i can already see a few problems here... i think you may have been given some bad advice by the shop you got them from (not your fault). ill explain the isues here....

firstly: the fact that you are keeping goldfish and neons together. goldfish are coldwater fish, neons are tropical, and the two should never be kept together under any circumstances. sometimes, certain tropical fish can be kept in more temporate conditions, but they merely survive, not thrive, and besides, neons are not amongst these fish as far as im aware. plus, when the goldfish grow, they will eat the neons.

secondly: your tank is too small by far for the stock you have. depending on what species of goldfish you have, you will need an absolute minimum of 50L for one single goldfish, up to 100L per fish for the larger species. if you have basic orandas or moors, then your fish will likely need about 100L of space. 200L for shubunkins and comets and the like. so even going by the minimum size, your well overstocked with just the goldfish.

thirdly and finally: Biorbs do not make good tanks, especially for goldfish. the filters on them are sub-par, and the lack of surface area means the tanks suffer from a lack of oxygen. with goldfish being big messy fish that require a lot of oxygen, they do not make suitable homes.

how long has the tank been set up for?

what id be inclined to do, is return the goldfish to the shop, and get a heater for your orb. a lot of tropical species are a lot smaller and less wasteful than goldfish, so should be suitable for the biorb if you go easy on the stocking. tropicals are no harder to keep than goldfish (in fact, many would say they are easier), they just require the extra heater. if you want to keep the goldfish instead, then you will need to return the neons, and upgrade to a better quality, rectangular tank. As it stands, you will not be able to keep your current stock in your tank for long, and you will face mounting problems as you go along.

sorry if any of the above sounds blunt. its not meant to be. im sure its not your fault, and you've been just misled by the bad advice so often given by unscrupulous aquatic shops who are only after your money.

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I've had the current set up for over 6 years and this is the first this has happened I have an additional filter in the tank as I was aware about biorbs filters.

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Thousands of years ago cats were worshiped as gods...cats have not forgot this !!!!