When you purchase them make sure you pick out some fat healthy ones, and if at all possibly pick them out after they have been at the LFS for a while; if they arrived that day and you take them home thats all the more stress they are going to have to endure - not very good odds of success.
having purchased alot of otto's I agree, however I didn't lose any of the last 6 I purchased and they looked terrible when I brought them home, I thoguht one of them was dead even! Some luck is definately involved.
I have an AWFUL diatom problem in my 10 gal, so I bought 3 just now! 1.99 US$ a piece. They are very, very little, so if they really do need 10 gal/oto, then I'll give the other two to my local fish store later..perhaps for store credit.
I had a 10 with really bad diatom issues..the oto's ived in it for over a year..with no issues..the big issue is as the tank matures..the diatoms become less of a problem and the oto's will need to adapt to a new food source. which can be difficult..
so even with diatoms you may need to add some other food to get them use to a different food.
I had a diatom problem in my 20 until I put an albino BN pleco in it; problem solved. He gotten bigger and it's a good thing I'm getting a 90 sometime in the enxt few months.
