Help My Fish Keep Dying

Help,  I've recently got an Askoll Pure tank XL.  Followed the instructions on how to set up a new tank and have put in 3  Harlequin, 2 Pakistan roaches and 3 cherry barbs.  Saturaday morning I found one of the harlequins swimming in circles with only one eye.  He died.  Went to Pets at home and got 6 x harlequins and 2 x bristle nose catfish.  Sunday morning another harlequin dead.  This morning another one dead and now another one swimming in circles with only one eye.  He's now dead.  My daughter who has kept fish for nearly 20 years thinks its to do with the oxygen levels in the water and the filter on this tank not being strong enough.  Does anyone know about these tanks and whether I should get a second filter.  Also, what is killing my fish?

If your daughter still has fish, ask her for some of the media in her filter, and put it in yours however you can make it fit. A sponge can be cut up. It must be kept wet in tank water all the way from her tank to yours. This won't instantly cycle the filter, but it will speed it up greatly.

What do you mean by 'let the tank cycle'? You don't let the tank do a fishless cycle, you do a fishless cycle by adding ammonia. Did you add ammonia? If you didn't, then you didn't do a fishless cycle, you just ran the tank empty for 3 weeks and you are now doing a fish-in cycle. Three weeks is very short for a fishless cycle. The one I did earlier this year took 7 weeks.
The fish will be showing signs of lack of oxygen because that's what ammonia does to them. It burns their gills making it difficult for them to breathe. Later when you have nitrite, that also deprives them of oxygen as nitrite sticks to the blood so it can't absorb oxygen. Nitrite does to fish what carbon monoxide does to us. Because their gills are burnt, and then because their blood can't absorb oxygen, they gasp at the surface, a instinctive reaction to them not getting enough oxygen into ther bodies.

Some loaches do have the reputation for attacking other fish. And like all other fish, they will be more aggressive if they are stressed. They are probably stressed because of ammonia in the water, because the tank is too small and because there aren't enough of them.
There is very likely ammonia in the water if your fishless cycle did not include adding ammonia to grow the bacteria. They need a tank with a footprint of 120 x 45 cm and your tank is 76 x 36cm. And they need to be in a group of at least 5 - but you don't have room for them.


The fish shop has given you some good advice (and that is quite unusual!) The best thing to do with the loaches is to give them away. Your tank is fine for harlequins and cherry barbs - once the filter has cycled.