A couple of months ago I set up a small 30l tank for my son with 6 minnows, a lone shrimp and 2 snails.
All but 1 of the minnows have grown well and are thriving. Tank was cycled, all levels are checked and good and I'm doing regular water changes. I have a fast flowing internal filter with plenty of surface disruption as i know the minnows like alot of flow due thier natural habitat. I'm feeding them premium flake food twice daily and add shrimp and snail pellets every few days.The one I'm worried about is much smaller and is often found milling around alone in the top corner behind the filter, amongst the plants leaves and most recently just floating near the bottom of the tank. If he's disturbed he swims away fine but his behaviour is so different to the others and his size is a real concern. Any ideas? I'm at a loss. I keep goldfish in my bigger tank but I have never had white cloud mountain minnows before.
Thanks

He's taken a turn for the worse over-night, he's sitting on the bottom, alive but struggling. I don't want to move him to a hospital tank and induce more stress. Dropped in a half squished pea and will do another water change but it does not look good. I know people they are only tiny fish but I care about all of them no matter how big or small.

Sorry to read about this.

While I've never kept minnows myself, I have noticed with shoals of different fish, that some seem weaker than others and behave exactly as you describe - sometimes these go on to survive and do well, other times they succumb. Your situation doesn't sound very promising, unfortunately, but, on the basis of what you describe, I actually think some time in a quieter-flow hospital/quarantine tank might not do any harm and might actually give the fish an opportunity to improve. Moving a fish can sometimes be stressful for a fish and sometimes not - usually the latter when they are already in a poor situation as you describe, when sometimes they almost seem to be relieved to be away from the heavier flow and other activity in the tank in order to build up strength and recuperate.

Do you have another tank/tub and filter (and heater if you're using one)? If so, you could move the minnow across into that, provided that the water temperature could be maintained at the same level as in the main tank, with a small portion of filter media from the main tank in its filter to ensure it's instantly cycled. It might even be possible, with frequent and large but gently undertaken water changes to minimise disturbance, to keep the minnow in that tank without a filter if you don't have a spare one. Placing a dark towel over/around the tank can help reduce stress if required.

Fingers crossed for this minnow; let us know how he gets on if you're able to move him into another tank.

If, however, he's succumbed, then you may find this article helpful
https://www.fishkeeping.co.uk/modules/ ... esheet.php?caresheetID=73 for that species' requirements and for the remainder of them in the long-term, in particular the need for a larger tank.

Thank you so much for your response,
I do have a spare filter and a small 20l tub i can place him in, I will add 10l from the original tank and get the water up to temp. Is 1/3 of the filter medium enough to put in the other filter? Hopefully a bit of time alone may help him the poor little guy, I didn't want to move him if it caused more stress but I think you are right that it's probably more stressfull at the moment.

I will keep you posted, thanks again!

That sounds perfect. Yes, anything up to a 1/3 of the filter media ought to be safe to move - in fact, a little less than that would be fine as it ought to be sufficient to deal with the waste he produces.

If you haven't moved him yet, then I'd recommend moving him via a jug (obviously a clean one, well-rinsed) rather than via a fish net. I find fish, especially ill ones, can be moved quite easily via a jug as they don't realise they've been "caught" as such, especially if you carefully manoeuvre it. A net can be moved from behind to guide him into the jug if need be.

Hope that helps - good luck, and keep us posted.

I managed to scoop him into a baggie and acclimatised him for 30 mins before opening the bag. I didn't want to net him anyway as he seems so frail. He's still swimming but is now hiding behind the pump, I've covered it over and will hope for the best! I've popped some food and bits of pea in and will check on him in the morning. Not much more I can do for now. Thanks for the help and I will update tomorrow.