[CeceliaJ]

I have a 37g column tank, dimensions are 20x18x24H.

I wanted to have a school of 12-14 small tetra or t. espei but is this footprint large enough? In addition to the school I would like a pair of German Blue Rams and possibly 6 Marbled Hatchetfish (already have a secure lid). 37g is a pretty good size but since I'm working with more vertical space than horizontal I want to be sure my tank can accommodate a small mid-level swimming school.

(Sorry about picture quality, taken with a cell phone)

 

[Nordic]

Start with some of your selection, and look at your ammonia/nitrite reading just before our regular water changes to see if your filtering can keep up.
I suppose you can keep an eye on dissolved O2 as well as that is the other limiting vector.

 

[sevendust111]

That is a large enough tank that you could do 12-14 of any kind of small schooling fish imo. I have 8 rummies in my 15 column and they are fine. It is not ideal, but they do ok. Neons, cardinals, harlequins, cpds, etc would all be fine.

 

[CeceliaJ]

I've decided to go with T. Espei, they have them at my lfs and from what I've read they seem more hardy than neons/cardinals and are still small. Now I'm wondering if 18x20 is big enough for marbled hatchets....