I don't cook it at all for the bigger plecos, but the youngsters have an easier time eating soft zuchinni so I nuke it for them to make it soft. Otos don't quite have the sucking power that the plecos do so personally I think softer is better for them. I've always heard that cucumber has less nutritional value, but the veggies should only be a part of their diet. I find the softer the zuchinni, the faster the filter gunks up, but when I'm raising baby plecos, that is secondary to their appetite and proper growth. Soft or non-nuked....I rarely leave it in longer than 24 hours.