Yes, you can use fish food to cycle a tank but this also builds up phosphates which can lead to algae outbreaks. Also, it is hard to control the amount of ammonia being produced from fish food. It would probably be better if you could find ammonia solution. Just make sure there are no additives in it like soaps, perfumes or other solvents. Shake the bottle and if there are foamy bubbles don't ues it, if not is should be safe. Also, check the ingredients list if you are unsure. You can get it at a hardware or grocery store I believe. The bottle will probably say 9.something% ammonia on it. Just add enough to bring the ammonia level up to 4 - 6ppm and try to maintain this level untill the tank is cycled - it is cycled when the bacteria can process 4 - 6ppm of ammonia in around 12 hours.