You have to cycle it first before you can only do water changes once a week. =] Would you like some info on cycling? =]
If so here's a great sticky thread
It looks like it would be great for a simple biological filter. =] I would adjust the flow a bit though because even though it seems like the current isn't strong, those bubbles actually move the water quite a lot.
A simple way to adjust the flow would be to tie one or more knots in the airline tubing.
Also is that a regular household sponge? If so then it most likely has fungicides, and other chemicals in it. The only kind of sponge you really want to use in an aquarium is a sponge specifically made for aquarium use.
A great choice as far as sponge goes is the AquaClear brand.
=] you can buy a box of three sponges for 30 gallon filters for less than $5.00
The sponges are pretty big so once you cut them up they should make a nice filter for you. =]
Also if you live near a Petsmart or PetCo, seeing as you already have the airline tubing and the airpump, why not go through less hassle and try out this product?
You could also pick up a 2 way airline valve
to help control the current. =]
These are all cheap if not cheaper than a typical filter seeing as the AquaClear sponge is only $2, the valves are only $2, and the filter is only $6 (when not on sale).
The only thing you really NEED to change is the sponge though. =]
The Current might become a problem in the future but it shouldn't be too bad considering you can knot your airline tubing if you don't get the valve. Also your boy looks like a veil tail and their tails tend to be more sturdy than those with more elaborate fins. =]