In general Prime is safe to use. But I find it expensive. My preference is GK Lloyd's Supachlor, which you can buy from our sponsor Techden. Cheaper, and treats lime in town water, heavy metals, etc.
One thing to note with Prime, but is unproven however there are many cases, is that Prime deprives the water of oxygen if you use more then the recommended dose. You might be using more to try neutralising ammonia, for example.
So if you had to use Prime in this manner and use extra dosage, watch for signs of oxygen deprivation, and aerate heaps.