I keep zebra otos which tend to require more food than normal otos (due to their larger sizes) and i regularly feed them blanched zucchini slices as supplement food too. The amount to feed requires some trial and error, as it depends on various factors like the number of otos and the algae content in the tank. For a start just put a slice in everytime they finish eating. Once you start to see the slices not get eaten then it means they have had enough and you can feed them less frequently.
Its always best to have otos that maintain a round belly, if you see any of them start to get flat or sunken bellies, then it usually indicates lack of food, which means have to increase food supply.
Btw, otos do go for algae and sinking wafers too, just that sometimes it takes newly introduced otos abit more time to realize that its a food item. What you could do is just put an algae wafer in a small dish every night, the next day remove it if uneaten, and then repeat again the next night. Once they are used to algae wafer they will rush to it as soon as you drop one into the tank.
Here is an example of how i put a slice of zuchinni along with an algae wafer together in a suspended acrylic feeding dish for my otos:
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