I only have 1 bare bottom tank, and that is because I don't feel like buying more rocks for a 3 gallon that I needed to get for a betta sorority emergency. I would post a picture but I am at work right now. In reality bare bottom tanks give your fish more room to swim. But if you're like me I want all my tanks to have some sort of garden look so I'll be putting in some plants later on.
Well a 20 will never have to be fully cleaned so I would say don't do it. It is beneficial to your tank as it is the #2 housing place for the bacteria, most is in your filter of course. I wouldn't o it as it may mess up your cycle, plus it just look better. Though in tanks that I would do 100%s I would have t barebottom.
I have a 20 gal without gravel. It's supposed to be a growout tank but I didn't get bunches of babies so Dizzy is in it all by himself at the moment. It's super easy to clean and I don't have a filter (other than a sponge which is currently off) and its not cycled. He's so happy he's built a big bubble nest.
The tank cycled with gravel, so taking it out probably isn't a great idea, you have several fish in there, including cories. If you really want to, you could take out 1/3 of it, wait two months, take another third out, wait two months and take the last third out. That should give it time to catch up. I'd put a thin layer of playsand for the cories, they really need something to nose around in.
I agree w/ Olympia...don't take it all out at once or it will mess w/your cycle...
Also, fish are accustomed to darker, less reflective bottoms...it makes them feel safer and they might get nervous and always attempt to hide...some fish act a little crazy w/bare bottom tanks.
In addition, no substrate can limit what plants you can have...all my tanks are dirt substrate covered w/black sand...I love Natural Planted Tanks, and evidently so do my fish since everyone is having babies w/o consulting me and w/no help from me!
Internal filters can't have sand, most hang one are fine, just keep the sand low enough that the flow doesn't disturb it.
Also, don't buy dark "tahitan moon sand", to my knowledge it is all made from glass shards which can inbed themselves to your cories, buy playsand at home depot.
I use just plain old aquarium black sand, which also comes in reddish brown and white/cream, from Petco. No problems noted with any of my fish...in fact, my bettas love it as much as my cories. Daffodil lays on it w/fins spread and head slightly up as if he is in a lounge chair enjoying the sun! Of course, he also sits in a baby crypt(type of live plant...easy to care for and loves low to medium light) and spreads his fins so that it looks like he is in a throne! No damage to his body has been found.