Hey All, After recently getting settled in new living arrangements, and getting married (tomorrow is the 1 month mark), I am really getting back into the hobby. The niece and nephew love fish, and love the Betta we currently have. Prior to this, I had a couple of tanks over the course of a few years in my teenage years. Currently: 5.5G Heated, Filtered (AC20) Betta tank. The plan we had, was to start a community tank. I had forgotten enough about the hobby and fish's requirements to think a 5.5g would be enough for a betta and a couple compatible tankmates. Now I know he needs 5g all for himself, and other than some shrimp... that this 5.5g is just enough for him alone. Hes been happily thriving in that tank for a couple months. So, once my discounted Petsmart giftcard gets to me this week, I will start building a 20 long to house the betta and a couple varieties of compatible tankmates (Niece and nephew will be choosing - with help from us and the LFS staff). Likely a couple of schools, so, ~12 fish in addition to the betta. If the betta acts up, he will end up in the 5g in my office. Questions: 1. AC20 in a 20 long - is it enough? Or should I get a small sponge filter for additional surface agitation+filtration. Any reccomendations on a small sponge filter (I have amazon prime if that helps). 2. I like dark substrate, and some of the fish the niece/nephew like also like darker substrates, I have read. Any thoughts on the bagged petco sand? Otherwise smooth/smaller darker natural pebbles (reccomendations?). I do think corydoras will be one variety in the tank. 3. I see very conflicting opinions on corydoras. From some saying "a couple in a 10g is fine" to "nothing smaller than 30G and 8+ corys". I do know they like company, so 5-6 are going to be purchased anyway, but thoughts on tank size? 4. Cycling and using an existing filter. Betta tank has the AC20 currently for about a month, precautions or suggestions before bringing to the bigger tank? Thanks!