Yeah, many ottos tend to die. IME and based on what others have said as well, if Otos are going to die, it will actually be several weeks after introduction, not usually within the first few days like other fish would. They eat biofilm and algae that you can't really see, not hair algae or beard algae or mossy algae or anything like that.
Mine tend to prefer blanched zucchini over other veggies...spinach is messy when blanched but they did like that too, and even hung around on cucumber a bit. IME, if you go a while without feeding veggies, they forget what they are and it takes time to acclimate them back, just in my experience though...(I have plenty of algae)
They also like hikari algae wafers a lot, but my snails cover them too quickly haha!
To put it simply...zucchini is my go to, they love it...my 3 champs that are my original otos have lost their appetite for anything except natural algae...good thing I have plenty of that!
I place the blanched zucchini at mid level around in the early/mid evening and remove it in the morning before it disintegrates and causes a cloudy mess, if it's blanched just right, it won't last much longer than 12 hours. Hope my experiences and thoughts help, I love otos. Don't be discouraged if half of them die within the next month, it's not your fault. (Probably....

hehe jk)
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