lovell_89 said:
the tank holds about 13 UK gallons, its been set up about three weeks and these are the first fish to be put in. its got a bio filter and carbon filter and ive have used dechlorinator.
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The tank is cycling.
Basically aquarium fish are essentialy living in their own toilet and their poop amoung other waste produced in the tank creates ammonia, which is lethal to the fish in any small quantitys, so what do we do to get rid of the ammonia?
There are beneficial bacteria that live in your tank filter that can break down ammonia into harmless substances but when you buy a new filter/set up a new tank it has none of this beneficial bacterial so when we cycle a tank we are basically trying to build up enough good bacteria in the tank filter to help break down the ammonia and keep the tank and fish healthy.
Tap water contains chlorine which kills the beneficial bacteria which is why you dechlorinate the any water that goes into the tank or is used to clean anything in the tank as the dechlorinator removes chlorine and other harmful chemicals present in tap water to allow the good bacteria to survive and keep your tank clean and healthy.
There are quite a few ways you can cycle a tank but since you have fish you will have to opt for cycling with fish unless you rehome them, cycling with fish can take quite a few months before the tank is totally stable.
You have the filter and dechlorinator but you will need test kits for ammonia, nitrites and nitrates to moniter your cycle and to avoid too much ammonia or nitrites building up in the tank.
Ammonia and nitrites should be 0 in a cycled tank with no exceptiones while nitrates should be 40 or under. If there is ammonia present in your tank you need to do a water change, if there is nitrites and/or ammonia present in the tank 60% water change should be done imediatly. If you have nitrates over 40 you can add more live plants to the tank to lower them as plants take up these or simply do more water changes.
For a mature well stocked tank most people do a 30% water change once a week but for a cycling tank with fish i'd advise a 20-30% one every couple of days(there are some pinned articles on cycling tanks in the beginners section for more info
).
Your fish are acting ill because the water quality is going bad and this can be sorted out with water changes
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