Just take an ordinary pint jar and fill it either with water from a filter that has been in a tank going for at least a year, or more easily pull over to the side of the road and gather some water from a canal or pond. Go to the grocery store and buy a turnip. Yes, a turnip. Peel the turnip, cut the white inside part into small 1/2 inch squares. Take the pint of water and drop two of these squares into the water,they will float like ice cubes. Eat the rest of the turnip, they are very healthy and taste wonderful raw. After 5-6 days the turnip pieces will have started to decompose and will be filled with visible infusoria. I take a three cc syringe and put the open tip onto a floating turnip cube and push it gently just under the surface drawing water into the syringe from the side of the turnip. If you take a clear shot glass or similar vessel, and fill it with the water you just gathered from the turnip cube you will see hundreds if not thousands of tiny one celled creatures moving about. Simply dump this into the fry tank a few times a day. On keeping the culture going, just get a second pint jar, fill it with water from the aquarium, put two cubes in it, wait two or three days and draw out some infusoria from the first jar to inoculate the next. You can keep cultures going till the end of time like this. ** The advantage of doing it this way is that you will always have a clear culture, no green water, no stink, perfect culture **