Stocking An 8 Gallon (30x8x8in)

[mantella]

I presently have a 8 gallon populated by 12 Nannostomus marginatus. I have had quite a bit of trouble keeping the tank warm enough because of it's placement, which can't be changed, and the narrowness of the water column. I even have two heaters (40-50 watt) on it. I recently obtained some Pygmy Corydoras who promptly croaked from a combination of some excess food waste (which I did not know about until later) and the coldness of the tank. This incidence has convinced me to return the marginatus and get some coldwater fish (I'll be keeping one heater in to stabilize the temperature). I'm pretty sure White Cloud Mountain Minnows fit the bill, but what other options do I have for an 8 gallon?

 

[techen]

Why are you having trouble to heat a tank? Surely move to a 100w heater?

 

[GoldfishLove919]

A good rule of thumb is 1 inch of fish per 1 gallon of tank water.  You might want to be careful to not add too many fish.