[FONT="]Yet another reason why you do not blindly trust pet shop workers
Anyway, it's good that you are returning the minnows, as for the cories - if you can't change all of the substrate then you can add a layer of sand, or a smoother substrate on top of the one you currently have so that they aren't in direct contact with the gravel. Or just remove and replace part of it, it's better than nothing. You can create an area of the tank that has only sand, as a sort of "play area" for the cories. They enjoy digging and playing around in sand, they are typical bottom dwellers. Smooth and rounded gravel could theoretically be OK, but they are definitely happiest when kept on sand.[/FONT]
[FONT="]Don't worry about the betta's fin - even if part of it fell off, it should regrow in time. The fins don't look infected, there isn't anything growing on them or any visible soreness, and that's a good thing. They just look kind of stiff and torn. I don't think he has active fin rot right now. Maybe try looking into fin melt – he seems to be showing some symptoms of it (the fins have a bit of a “melted plastic” appearance). Try showing him a mirror, see if he is able to flare. If not, then I think I had a similar problem with my betta a while back, his fins were very stiff, clamped and had holes in them (and he was unable to flare), and to this day I'm not sure what caused it (probably water quality + some kind of bacterial infection). I cured him with daily dips (in a separate container), first in salt (for a few minutes), and then in this product:
https://www.amazon.co.uk/Tropical-Healthosan-Health-Treatment-Bacteria/dp/B019J5GTVK (for several hours at a time) - I did it every day for I think close to a month (+ regular water changes and a constant supply of almond leaves), and in the end the problem went away. If you’re curious, I've got some before and after videos of him: [/FONT]
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- the fins look almost “melted together”[/FONT]
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