Just remove the seeds, if any, insert a fork between the skin and the flesh and blanch (boil) for several minutes in a sauté pan. Let cool and drop in. Leave no more than 24 hours. You can also use orange, cucumber and most lettuces. Certainly not ridecio etc.
Thanks Lisa, from your above reply I am guessing you use the spoon to sink the food? I put raw courgette in tonight and its floating so just about to take that out and throw it. Have boiled a slice thinking that would make it sink but I am guessing thats going to float too now. I don't have a spare spoon for the fish tank, the Mrs will kill me if she finds me using our dining cutlery in the fish tank