Sizo of sponge filter?

[Ron]

Around wha size sponge filter should use for my expected betta fry? I'm going to have them in a 5 gallon, for teh first couple of weeks, then move them to a 15 gallon. What size spnge filter would filter enough water per hour for these two tanks. Also, do you have just a estament on how much that would cost. I have 3 days to get everything situated for the spawning. Thanks,
Ron

 

[Alien Anna]

The smallest size is fine, provided you've colonised it with beneficial bacteria (suspend the sponge section or the whole filter in your main tank for a week or more).