Thanks. I didn't want to have them in the smaller tank any longer than necessary, so they went in the bigger tank immediately, filled fresh water from the tap. There is a filter but I had some issues with water leaking because of the filter, I need to fix that, so it's not running at the moment. I think I should be able to make it work properly tonight. So far I've bought 2 batches of feeder fish, the first one was really bad, massive amounts of them died before I could even feed them. Now I'm using a little pond outside that belongs to restaurant down my appartment as feeder fish pond, but still quite a few die every day. I do feed them, so I'm not sure why so many die. Maybe next time I leave the bag in which they come in the water for a while, to acclimate them. I don't enjoy having to get out all those dead feeder fish every single day too much.