You don't need to do a WC now. You want to keep them around .25 ppm until the tank cycles. As I mentioned before, you need some ammonia and nitrite to build the bacteria colony. You just don't want them to get out of hand and harm the fish.
As far as tocxic ammonia (or free ammonia) is concerned, you can use the chart on this page to calculate it. To use it, just cross referene your pH and temperature and multiply your ammonia reading (.5) by the number you find on the chart. So if your pH were 7.0 and the temp was 79, then you multiply by .006. That would mean that your toxic ammonia level is .003 ppm. The lower the temp and pH, the less toxic ammonia you have. Of course, with lower temp and pH, the slower beneficial bacteria multiply and reproduce.
As far as tocxic ammonia (or free ammonia) is concerned, you can use the chart on this page to calculate it. To use it, just cross referene your pH and temperature and multiply your ammonia reading (.5) by the number you find on the chart. So if your pH were 7.0 and the temp was 79, then you multiply by .006. That would mean that your toxic ammonia level is .003 ppm. The lower the temp and pH, the less toxic ammonia you have. Of course, with lower temp and pH, the slower beneficial bacteria multiply and reproduce.
