I have 2 goldfish, 1 black moor, 1 blue oranda and 3 danios in my tank. I did my first clean/water change last night and ever since one of the goldfish has been acting really weird. Last night it got itself wedged between the back of the tank and the filter and stayed there all night (I presume as it was still there this morning). It came out just before I went to work but when I came home I couldn't find it anywhere...then realised it was hiding in the wooden barrell and hasn't come out since I've been home - even when I fed them.

Any advice?

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Ok, before we can help you, we will need to know the following details about your tank

size:
is the tank filtered?
if so, what type of filter:
how long has the tank been set up?
have you done any water tests?
if so, what are the results (at least for ammonia, nitrITE and nitrATE)

the behaviour you describe could be one of many things, so we need to know as much as possible to narrow down the cause. one thing i will say though, is remove the danios, cos the goldfish will eat them sooner or later. danios do not make good tank mates for goldfish!

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It's a fluval filter, just like the ones in the tanks in most pet shops. It's been setup for about 5 or 6 weeks. I treated the water with the stuff to make it safe and remove any chlorine etc. Got the goldfish just over 2 weeks ago and the others a week later. Was told I could have danios as long as they're not too small?

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I would guess that you have a fairly seious nitrite problem now

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Why? None of the other fish are acting strange...

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When water quality issues hit, they tend not to obliterate every fish within seconds of each other. Different fish have different immunities, even within the same species, and if you’re looking for an inconsistent indicator of whether things are going well in the tank, then basing it on the wellbeing of the fish that aren’t dying is one terrible way of going abut things. the other fish may be "fine" for now, but for how long.

basically, your tank is very new. generally, we wouldnt advise adding fish to a new tank for about 4-6 weeks at least! this is because this is how long it takes for benefitial bacteria to grow inside the filter, to a level where they can safely devour the waste produced by the fish. and even then, you cant just leave it to sit and wait, because the bacteria need food. during this innitial 4-6 weeks, you need to be adding something to the aquarium for the bacteria to eat and grow, such as uneaten fishfood, or household ammonia.

basically, what im assuming has happened here, is youve not left the tank long enough, and you have added the fish to a tank that simply wasnt ready for them, due to a lack of bacteria. no bacteria means no waste removal, and so the fish will be swimming in their own toxic waste, making them very ill.

have your water tested, for at least ammonia, nitrite and nitrate (most aquarium shops will do it for you), and have them write down the results so you can post them here (one rule with fishkeeping is to not listen much to what retailers say, they will try and sell you anything, so dont let them try and sell you stuff to help you yet). in the meantime, try and carry out 50% water changes daily, as a way of diluting any toxins in the water.

also, might i ask as to the size of the tank?

and finally, dont feel bad about this. its a trap so many new fishkeepers fall into, and in no way do we blame you for it. its not your fault. im guessing its a combination of bad advice from the shop you bought them, and the myths that have festered in the hobby. all you need to do now is ensure you do whats best for the fish and try and help them

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I had a similar problem. I had 4 goldfishes in 1 tank about 5 gallons. as this is the first time I am keeping fishes, I followed other people's advice. They said it is very easy to care for goldfishes and they do not need any special care. So I filled the tank with "2 day" water, added some stones, and 2 days later 2 of them died. I don't know why this happened? I think I did something wrong.

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