Ordering Fish Online....meh

[DerpPH]

Both Wills and Eaglesaquarium are very knowledgeable posters, as are many of the other posters in this thread.  I didn't mean to contradict anyone's advice, only adding my firsthand experience with these awesome fish.  I also use Seriouslyfish as a major reference point as well as Planetcatfish among others.
 
I would also recommend the Pristella X-Ray Tetras.  They can be kept in a much smaller tank than the Glass Cats and they are available in the standard X-Ray coloration as well as an albino strain known as the Gold Pristella Tetra.  Strangely enough the Gold variety is is roughly half the price of the X-Ray and just about the same in transparency.  The Gold Pristellas that I recently added to my son's 55 gallon kinda glow also, which looks great against the greens of the plants & the black background.  Glass Catfish cost about $5-7 each, while the Gold Pristellas are only $1.89 at Petco here in North Carolina.  These are shoaling fish that shouldn't be kept at less than 6 specimens and more is always better.
 
If you decide to get Pristella Tetras I would say you could fit up to 10-12 in a 20 gallon, of course depending on what else you keep in that tank.  Since the Gold variety is just a color morph of the X-Ray, you could keep a shoal with half of each much the same as keeping Tiger Barbs, Green Tiger Barbs & Albino Tiger Barbs.
 
Back on topic:  Glass Catfish are one of the worst types of fish to order online since they require swimming room.  It's safe to say they won't get that room in transit to your address so there's a good chance of getting fish that are very stressed and aren't healthy.
Gold Pristella Tetras:
 

Id disagree on the 10-12 fish in a 20 gallon part. They grow to about 2" and need some space to grow and move about. Like many tetras... Id say a shoal of 6 would be alright but i think you can get away with 7-8. They need the a bit more space than cardinals or neons. Btw do quarantine the fish you get

 

[Ruskull]

Again, I'm not here to argue but to give firsthand experience as well as pass off some knowledge I've gleaned from the internet on the particular fish being mentioned.  Some internet sources claim that these Pristellas are okay in a 10 gallon tank, but I wouldn't agree because they are fairly active fish.
 
BTW, Seriouslyfish site says a min. tank footprint for these guys is 60cm x 30cm, which is roughly 24x12 inches and the exact footprint of a 20 gallon high.  A 20 gallon long is roughly 30x12 inches. 
 
A 20 gallon high or long should be large enough for 10 Pristella Tetras, 6 Cardinal Tetras, and 6 Threelined Corries or a similar sized Cory.  This would not be an overstocked tank by any stretch, especially given the fact that the threadstarter does frequent water changes.
 
These Tetras do not grow to 2 inches either, more like 1.5 - 1.75 inches including their tails.  Cardinals & Pristellas certainly do not have a large bioload.
 
I'm not sure that Pristellas are okay to be kept with smaller, thinner bodied Tetras such as Cardinals though, as I've never kept the 2 together.  I keep my Pristellas with larger, slightly more aggressive Tetras like Black Phantoms, Lemons & Von Rios.  The Lemons are the most aggressive of these mentioned in my experience.  

 

[Noahsfish]

I really do like those pristellas, it'd be nice to have a school of fish other than cardinals. Thanks for all the great advice and suggestions, but I still feel like I need something to finish my tank. If I do go with pristellas tetras what would be a good centerpiece other than a betta. Or, if the pristellas fully stock my 20 gallon with their required school would this stocking work?
X5 cardinal tetras (fully grown)
X6 pristella tetra
X6 sterbai corydoras

I was going to get more corydoras, but I think I'll stick with 6 for now. And if anybody has any advice to give on my current stocking idea than that would be appreciated, but the cardinals and corydoras have to stay in the 20g for now.

 

[CJH0825]

I just recieved a order from Liveaquaria.com and I must say, I thought the shipping cost was rather steep, but when I received my package, It was in excellent shape! They took exceptional care when packaging! I'll be ordering more from there very soon!

 

[Ruskull]

I really do like those pristellas, it'd be nice to have a school of fish other than cardinals. Thanks for all the great advice and suggestions, but I still feel like I need something to finish my tank. If I do go with pristellas tetras what would be a good centerpiece other than a betta. Or, if the pristellas fully stock my 20 gallon with their required school would this stocking work?
X5 cardinal tetras (fully grown)
X6 pristella tetra
X6 sterbai corydoras

I was going to get more corydoras, but I think I'll stick with 6 for now. And if anybody has any advice to give on my current stocking idea than that would be appreciated, but the cardinals and corydoras have to stay in the 20g for now.

 
 
You could go with that stocking plus a Dwarf Gourami or Fancy Platy as a centerpiece.