Hi all i am about to order some dividers but would like to know how many dividers i should get.What could i divide a 18x12x16 tank into? 3 or 4 compartments?
You can make super cheap dividers using plastic craft canvas and report cover plastic binder thingies. Just use aquarium sealant to fasten two report covers on either side for each divider, let cure for at least 48 hours, cut plastic canvas to appropriate sizes (make tall enough so that bettas can't jump over) and slip them into the report covers to hold them in place.
Here's the best pic I have of it, don't mind the gross brown algae growing all over the dividers.
You can even do something cool like attaching java moss to the dividers, I think that'd look pretty spiffy.
It may be a little cheaper to make the dividers yourself, but I prefer to use retail dividers since they're pre-cut to the proper size. The Penn-Plax dividers (sold at PetSmart and probably other places) are the ones I use, and they're very good.