enough filtration?

[longhorn13]

i've got a male betta in a 5G with a small sponge filter and one of those red sea nano filters. the nano say's it's rated up to 3G (i think) so will that and the sponge be sufficient? also, i was thinking about changing the substrate from gravel to sand so i could add a couple or three cories to keep him (and me!) entertained. would the same filtration i have running now be enough if i want to add the cories?

 

[cutechic]

That's definitely enough filtration for just the betta. I think adding corys would make the tank a little underfiltrated, but if you only add a pair of them (not 3) and keep up on your water changes, it shouldn't be a problem. I'd definitely change the substrate to sand though.