I used it as well as biospira. it is a bit more expensive . I used everything I had in the fridgeIf they are high enough they can. I wouldn't introduce a fish from a low nitrate environment to a high nitrate environment and not expect something. If it's in the 10-20 range, you're probably safe. Fish can tolerate high nitrates, especially if they rise in a tank over a longer period of time. Some people can test in the 100+ range and things look and act fine in the tank.
If you ever need to cycle a tank again, check out Dr Tim's One and Only. Its a great bacteria product. Used it to cycle my 220g when I set it up. I dosed enough for 280g and had the cycle done in 6 days. It will definately be more expensive then the bio-spira, but I liked it as a product better.