small tanks maybe a 2 or 1, u would probally rathe rhave the 2 and then point the current to an angle so it is not blasting if to powerful, but that way u have the more powerful powerhead when u upgrasdewhat one would be good for a 29 gallon with an S. Irritans in it?
Im doing the same and its a great powerhead to eliminate dead spots and to allow filters to pick up all water and not leave any water thats sitting in dead spots.I have a model 4 for my 6' 125 gallon. Sends a nice broad stream about halfway or more across the tank. Excellent product!!!