I had the same with my kribensis. I got two female and the guppies started being killed. Had to empty the tank to get one of them out (thank juwel with your secret hidyhole in the filter bottom). Got rid of them and then the moonlight gouramis matured and started ripping the guppies to shreds.
Hi everyone, I'm hoping someone can advise me on what I need to do with some aggressive danios. I've got a Juwel Lido 200 litre that I've been running for a number of months so it is fully cycled but a few weeks ago I got 3 albino danios and 3 zebra danios. The zebra danios (and one in particular) are being aggressive to all the other fish in the tank. They are not nipping but are chasing and hassling the other fish (peaceful community fish inc guppies, neons, corys, rasboras and a couple of dwarf gourami) so they can't get on with whatever they were doing in their own fishy lives and constantly have to look over their non-existent shoulders for the bullies.
I've had enough of them this evening and the 3 zebras have been relegated to the tiny 18 litre quarantine tank. I know it's not a suitable permanent home (anyway I need it as a breeding tank for my amorous rasboras) but I'm not sure what to do next. Will the equivalent of being sent to the naughty step make any difference? Do I need to get more danios so they school more?