Active Carbon for Aquatic Use

How much did your fish cost?

I'd go to a pet care forum and ask them.

Perhaps pure hardwood charcoal, but definitely not the processed briquettes. They contain some chemicals that might be harmful to fish. I wouldn't take the risk.

If the briquets have lighter fluid built in, will the neon tetras glow brighter?

I am assuming your are trying to mitigate the pricey A-Carbon filters rather than building a barbecuarium for your fish, since you didn't mention throwing some T-Bone steaks in there and filling it with cold Budweiser.

Zeolite it pretty cheap, and the type mined in the US is good at removing ammonia and other contaminants from water. It has a very high surface area for adsorption, but not as high as A-Carbon. You might want to use it as a prefilter before the carbon filter as this will give you a much longer life on the carbon. Also, the zeolite can be re-used, I believe, as it does not require being recharged like carbon filters. But it's so cheap, why bother. I understand from a friend involved in the N-disaster in Japan that they are pumping the stuff into the flooded reactors to trap a lot of the radiated nasties from the million or so gallons of water sitting aglow.

Also, you might consider a small UV light filter which is a simple DIY project. LED's area available for this purpose...mind the shielding so as not to expose the little fishes or their owner to UV radiation or they could go blind and not be able to find the charcoal lighter or the cooler.

Out of curiosity are you in the Kentucky neck of the woods? Good luck little fishies.

Would UV light filter destroy useful bacterial, such as nitrifying and photosynthetic bacteria as well?

Of course they would be destroyed, if they were subjected to the proper UV light source for sufficient time. But the colonies which are existing in areas that are not subject to a UV source would still be alive and there would still be the benefit of these colonies in the nitrogen process. If your filtration system is doing a good job of filtering out the nitrogen from waste, uneaten food etc. then the number of beneficial microbes decreases.

It's about maintaining a balance so an algae bloom is avoided which will turn any aquaculture toxic. This is true for in-home systems as well as mother-nature systems like Diamond Lake here in Oregon. This otherwise pristine lake was overrun with the tui chub that feasted on the beneficial algae leaving the blue-green algae to bloom, creating a dead lake.

All good points from Oregoon.

I just went through the process of starting a new aquarium (nothing extraordinary, just a little 10 gallon unit), so let me share some of what I have learned... and maybe save someone the frustration I went through.

Charcoal filters are unnecessary in a healthy tank. Only a basic particle filter is required, and it need not be changed regularly, only rinsed-out when it gets clogged. Even then, it should be rinsed in treated/conditioned water. If the filter must be replaced, let it float in the aquarium for a day to allow the bacteria time to inhabit the new filter.

If you do desire a charcoal filter, activated charcoal is pretty cheap when purchased in bulk. I paid about $10 for a pound -- and that was at a pet store.