can rummy nose tetra and black phantom tetra share a tank

Question
I bought 6 black phantom tetras and 6 rummy nose tetras yesterday afternoon. This morning three of the rummy nose tetras were dead and a fourth one died later. The other two didn't look overly happy and it looked as if some fins were damaged. The black phantoms were fine. The tank is an aquaone 126, which holds approx 22 litres. a possible problem is that the pump is too powerful since 1 or 2 of the dead fish were stuck to it. The tank had been running for a while (a month or two) before i bought the fish. Can you please help explain what went wrong and what i should do next?  

Answer
Dear Gerard,
1. No problem you can keep these two categories together.
2. The speed of you filter making trouble for them surely.
3. Change the speed immediately
Thanks. Good Luck.

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