Hi. Dont know what info you are going to want/need to try and help me, but here goes. I have a small 20 litre tank. Got filter and aeration. Started with 2 american flags, comet(?) 2 danios. 1 flag dies and comet. Then got fantail, and few weeks later that dies! recently had 1 American flag, 2 danios, 1 shubunkin?,1 goldfish, and loach. first shubunkin dies, then loach. Done water change with water safe, now goldfish died, and 1 danio on its way out! Have water test kit, and been monitoring every week. When shubunkin and loach found dead, n02 and n03 were way too high(but went from fine to that in space of 3 days!!??), which is why i did water change. what is happening here?? possible causes anyone?? my little boy has been very upset, and its costing fortune!! is tank too small?? HELP!! please...
Unfortunately you have a huge combination of problems: most importantly the tank is too small to keep any fish in, and Goldfish especially. Have a look at this article which explains the size Goldfish grow to and the size of tank they need (140 litres just for one long term).
Next your tank doesn't seem to have been cycled. If the tank isn't cycled then when fish go in they are poisoned by their own waste. With a tank that is too small for fish and a huge amount of fish all added at once, toxins would build very fast causing sickness and death. This article explains the nitrogen cycle and fishless filter cycling which involves dosing the tank with ammonia and testing daily for around six weeks before fish go in.
The other issue is a mix of incompatible fish species'. Fancy Goldfish (like the fantail) should only live with other Fancy Goldfish (in a big enough tank). Comets and Shubunkins are really only suitable for ponds as they grow so big and need lots of swimming space. American Flag Fish are aggressive and don't mix well with many other fish, or with each other. Danios are fast moving shoaling fish who need to be in large groups in a 3ft tank to do well. Almost all loaches are tropical fish, not really suited to cold water tanks and shouldn't be combined with Goldfish.
Sorry to hear you have experience such a bumpy start to fishkeeping
I wonder if the shop where you bought the fish from would take them off your hands whilst you source a bigger tank and get it safe first, before any fish are added?
Flagfish are generally very grumpy bordering on aggressive and don't make very good tank mates even if he does pull through.
As Fishlady has already mentioned, a small shoal of tropical fish need about 60 litres min, fancies, being the poop machines they are need about 180 litres for just two. These fish grow fast and quick, putting on up to 8 inches minus the tail in the first two years.
As tropical fish stay smaller, would you be prepared to add a heater and start with those. A 100/120 litre tank gives you some scope for 2 small shoals.
The next thing (only with an empty tank though) will be to then add a source of liquid ammonia to replicate the fish waste - think of it as your invisible fish - for 4 weeks or so whilst the filter builds up/grows enough bacteria to consume the ammonia that all fish produce.
Any questions at all fire away. I appreciate it can be a bit of a steep learning curve when you start.
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Oh dear that doesn't sound good I'm afraid It could be a form of fungal infection (saprolegnia) or possibly flexibacter columnaris infection. Either of these is possible as they are often triggered by poor water quality. There are treatments that sometimes work, but they mean not changing any water for several days whilst the treatment is used. As the tank is not cycled and toxins are constantly building up, water changes every day are essential at the moment so while medication might help with the fungus, the lack of water changes would probably finish him off. Sorry to sound so pessimistic, but that's the most likely scenario I'm afraid.
If you want to give treatment a go, the medication I would recommend for this is eSHa 2000. This is dosed for 3 consecutive days with an initial dose based on the water volume and then half that dose on days 2 and 3. It should be possible to continue with water changes by calculating how much of the medicine is removed by each water change and adjusting the next dose upwards to compensate. I can help with the calculations if you decide to try, but don't be surprised if he doesn't last 'til tomorrow