Hi there im new to tropical fish. i brought a tank of a friend
however it did not have a heater it did have a filter and a light on the top it is a 46 Litre tank. So i cleaned it properly and i have left it for about week and half with filter on to let it filter out the water. I then brought a heater and left it on 24 degrees C for a couple of days for it to heat up. I then went to AD Aquatics to buy some Water conditioner i put it in the tank and left it for a couple of hours then i went to the shop and brought some fish as they said i could. The man who worked there recommended some fish so i got them i got, 1 black Assorted Molly, 5 Cardinal Tetra and 1 Red Wag Platy, i also got another fish however i dont know what it is i beleive it is just a Assorted Platy. Anyway i left them on top of the water for 45 minutes to get use to the water tempature then i let them in the tank. However one of the Cardinal Tetra just droped to the bottom it was still alive however was really struggling to swim, after a couple of minutes it just died. 2 days later which is today all of the Cardinal Tetra have died apart from one and one was stuck against the filter with a ripped stomach however i believe this was due to the filter force. However all of the other fish seem fine swimmg about as normal but the 1 Cardinal Tetra seems shy just staying still most of the time is this as it is on its own becuase done Cardinal Tetra stay in packs. But apart from that all the other fish seem fine. Also my bulb has gone and is not working could this affect the fish and could this be related to the deaths . PLEASE HELP I DONT WANT TO LOOSE NO MORE FISH.

Hi and welcome,

It sounds like the shop you bought fish from have given you some very poor advice. The first problem is that what actually deals with fish waste and makes water safe for them is bacteria that grow in the filter and process their waste into a safer form. It takes 4-6 weeks to grow enough bacteria to do this by adding pure ammonia daily to encourage them to grow and "eat" the ammonia. This is called fishless cycling - see article here.

If fish are introduced to a tank before it has been cycled, they immediately begin producing ammonia and as there are no bacteria to process it, the fish are swimming in toxins which will make them ill and eventually kill them. If this happens, there are only two ways to save the fish: either take them back to the shop and cycle the tank before getting more fish, or follow these guidelines for how to do a fish-in cycle. This will involve testing the levels of ammonia and nitrite daily and changing some of the water every day to keep the levels low enough until the cycle is complete. This may take many weeks and is not guaranteed to keep the fish safe, so taking them back is the better option.

Either way you will need a good, liquid based test kit such as this one to follow the cycle's progress.

There are some more problems though. The fish you have all are really too big for a 46 litre tank. We recommend at least 60 litres for a shoal of small fish like Neon Tetras. Also, the fish you have all like different water parameters. Cardinals need very soft water with a pH of about 6.5 but Mollies need very hard water with a high pH around 8. Platies are somewhere in the middle. Your local water will not suit them all unfortunately. On top of that, Cardinals are very sensitive to both incorrect parameters and to the presence of ammonia, nitrite or high nitrates in the tank, which is why they are the first to show signs of sickness.

I honestly think the best answer for you is to take all the fish back, do a fishless cycle and while you're doing that, check the hardness and pH of your water supply so you can choose more suitable fish. If your water is suitable a single male Siamese Fighting Fish is appropriate for that size of tank, or some of the very small shoaling fish such as Celestial Pearl Danios or Ember tetras, or shrimps.