10-02-2008, 04:05 PM
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Umm... you got some real bad advice.
There's no reason to replace the sponge or the Biomax, well, at least not every other month. You need to do maintenance but all the sponge needs is a good rinse and a squeeze in some of your aquarium water and the biomax doesn't need any special care at all. The only thing that needs replacement on a regular basis is the carbon. In fact by doing this you're subjecting your fish to a mini-cycle once a month.
You don't want to keep the cycle going, you want it to end. You want to cultivate enough bacteria to keep processing the waste and prevent ammonia or nitrites from building up to detectable levels. By tossing out the filter media once a month you kill off half your bacteria and have to start recolonizing the filter.
As for your sand, cichlid sand is good for african cichlids, of which you have none. The pH of your tank is likely high because of that sand which only increases the danger of the ammonia. If you do replace the substrate don't buy stone from an aquarium store. Go to a lawn and garden center and buy pea gravel.