I really like the colour of the green ones, so I had 10 standard and 10 green in a Fluval Roma 125. My water is similar to yours
@Paddy60 and is 17dh. Unfortunately I didn't get all my fish at the same time, and possibly not all from the same place, and when I put them all together things were ok for a while (1 fatality in first week), but then I had a spate of unexplained deaths, with one fish dying each day, no signs of injury. Spoke to manager at MA and he suggested a treatment (which I think was for internal parasites, but can't quite remember), which seemed to help after a few days. I'd lost quite a few fish, and was down to 12.
Since then, one female was lost due to excessive hanky-panky related nipping. She was removed from the tank and quarantined to give her time to recover, which she did, but it all happened again when she was returned to the tank and she didn't survive the second time. That was a big disappointment as the pre-hanky panky related swimming antics were adorable, and I thought that things were starting to settle down.
In the past few weeks I've lost another 2 fish.
I'm stuck between reworking/replanting the entire tank and increasing tiger barb numbers to previous levels (too concerned to mix anything else with them), and giving up on tiger barbs completely (apologies for the defeatist attitude there), which is a shame because I really enjoyed watching them when things were going well as they are active and inquisitive fish with lovely colours and markings.
Spoke to one of the LFS staff and they suggested moving them to a bigger tank. I do have a Roma 200 in the spare bedroom which is currently empty. I had other plans for that, but the plans could change again if required.
I'm still very undecided, and will be following this thread with keen interest in the hope that I can pick up some useful information as well.