As entioned the male krib can get very very protective when breeding, Ive placed a terracotta pot in the corner of my tank for my kribs & breeding time, when it is that time you will notice the female will disappear completely for several days, the male will hover around by her protecting her and as soon as anything gets too close for his comfort he will chase them away, Ive not yet seen my male hurt any other fish as yet but it seems they have learnt if the cant see the female dint go nr the male. if you are lucky and you do get fry it is amazing to see the female aper with all the little ones under her belly and around her.
The Female krib is often the boss and in her world bigger is better !!! if the kribs haven't paired off themselves and she isn't happy with the male she has been given she will chase him off for a long time, eventually she will succumb to this is the best I'm gonna get time to make do, but for a while she will Chase him off, also sometimes when breeding, if she not in the mood she will let the male know, its funny to see my male chase of many fish bigger than he, and and not be hassled by other fish to then see him swimming scared because of his smaller partner.
kribs can be fun to watch, mine have turned out to be great landscapers, i never knew how much sand a female krib could move in one day and how much she cold hold in her mouth until i saw a big dip in the sand and a miniature mountain appear, at 1st i wondered what the ... is going on here until a tiny little krib head appeared at the the top of the hill had a cheeky peek around then spat out mouthful of sand then darted away only to come back and do the same thing over very 10 seconds
With otos they are very very sensitive to change, you need a well matured tank and even still for t he 1st few weeks of introducing Otto's you can loose some due to their nature. as said a fat Otto is a happy Otto and they do a great job if your having a Little outbreak of brown algae, i got my 3 Otto's as had a little bit of brown algae and within 2 days they had the glass and decor spotless and shining,