I've never had an octopus that small, but a piece of shrimp 1/2 the size of an octopus' mantle sounds like a lot to me. I suspect that an octopus will live longer if fed a small,but still a sufficient amount to slowly grow. I don't think it's been proven, but I'm going with that. I used to feed my 1/2 grown bimac every third day, which was enough for slow growth, but now I feed smaller amounts every other day. I found that the octopus would be less active (to conserve strength?) with the longer wait between feedings. I think that for a 30% grown up octopus you should feed as little as you can get away with, every 2nd day, while still seeing slow growth. That's a dangerous policy with a very small octopus like you have, because they don't have a lot of reserves and it's easier for them to starve, so feed every day for a while, and not too much. My octopus are kept cold (56 degrees) and probably don't need as much food as a warm water octopus like yours, so keep that in mind when you read my advice. Also, I feed both froze shrimp, and frozen scallops, which I think the octopus likes better. We think of scallops as expensive, but in the quantities that an octopus eats, they are essentially free, and make an easy way to mix up the diet a bit.