chemical consists of two pads? at least we make our own. i use blue filter pad 312' kind. and polyfiber. you can use aqua tech filter media in marineland penguin h.o.b.filters to save money.usually dont use carbon unless i need it, so i have more room for sponge/mechanical or ceramic-balls-stars/biological media. zeolite is better than carbon alot of the time and it is rechargable, by soaking in saltwater overnight. zeolite is good for getting rid of ammonia