This forum is full of experts, but there are also beginners and I still class myself as one. If one person learns from this then it's worth posting. I just lost a pleco and, I think, 2-3 shrimps, from adding avocado skin, with a little flash, as a snack. The fish adored it and I've added it a few times without harm, but I didn't foresee that it can be poisonous–my guess is this relates to ripeness, and a toxic element it contains. One to be aware of for those with good intentions.