Hello. In preparation of a tank upgrade that I'm working on, I just wanted to get some advice regarding these types of bottom dwelling species. Most importantly, I'd like some perspective on how hardy each is, compared to the others. I'm also lhoping to get some ideas on how well each would fit in with my current/planned stock. Cories: I currently have Emerald Green Cories. I like them, but they don't seem to be doing well, and I don't know why, exactly. Parameters don't seem to be a factor, and my thought is that I've had them for too long for it to have been as simple as I bought them sick, but not long enough for them to have died from old age (I've had them for several months). While aggression could always be a factor, I don't think this is my issue as I've never witnessed any other fish picking on my Cories. This leads me to wonder if they're simply not that hardy. I don't know, but any thoughts are appreciated. Hoplos and Pictus: I've never had either, but I like them both, and I'd like to learn more. With Pictus, I've heard everything from they're fine alone to they need to have a group of 6 or more. So, I'm curious to learn more about this, and again, just about any differences that exist, and which may be a better fit for me and my tank and why. This tank will be a 6' 100 gallon tank (upgrading from the 55 gallon I currently have set up) Planned stock: 3 Blood Parrots (currently have 1), 9 or so Nerite Snails (currently have 3), 10 Eastern Rainbowfish, 15 Congo Tetras, whatever I choose from the bottom dwellers list from above. I currently have 4 Emerald Green Cories, which is down from 8. So, my decision will be to rebuild my school of Cories (but I'm weary of this because they don't seem to be doing well), or to change to one of the bottom dwellers above, or some combination. Any and all recommendations and advice is appreciated. Thanks!