Bayea, Filtration for Bio-filtration does not require light, in fact most bacteria grow better in dark enclosures. But as far as building a skippy design for a tank, I'm not sure about that as well, It would almost need to be built higher than the tank itself to gavity feed back to the tank. I use magnum 330 canister filters on my 75 gallon aquarium and 30 gallon aquarium. been using all three (two on the 75 one on the 30) for well over ten years. On the 75 I do rotate cleaning one one month the other the next so as to keep the biofilter very active in at least one filter at a time, You would have to design some type of sponge or finer screen to prevent fry from being sucked in but that's a easy fix. as for stocking your tank, if possible make sure it has cycled completely just as you would a pond. Try not to stock a bunch of fish at the same time, Once your fully cycled, (4-6 weeks after start up in most cases) add a dozen or so fish, watch and monitor water quality for about 4-7 days, once it has settled do a small water change (10%) then add the next dozen or so. adding to many at one time can overload the bacteria, let them catch up to the load of fish. You don't want to have to change large amounts of water for the bacteria to catch up to a overstocked tank if it can be avoided. . Also it wouldn't hurt to add a bacteria supplement to your tank to help kickstart the bacteria, You are already doing this by adding filter media from an exsisting functioning filter. But adding a good bacteria supplement will give you better results as the bacteria bloom from the supplement will kickstart bacteria all in the tank, not just in the filter itself. Also most have enzymes added that help break down waste, this is good as it will help breakdown extra waste as your stocking the tank. Be sure and monitor your ammonia and nitrite closely, the fish and tank will dictate when it's necessary to do water changes.
