I'm no guru at all. In short I find it to be a good product.
I have used, and intend to use again,
API's Stress-Zyme, usually used and sold together with Stress-Coat, they are very good water conditioners in order to remove
chlorine/chloramines, and to add protective agents for the inhabitants of our tanks when performing routine partial water changes in allready cycled tanks. Of course you can use Stress-Zyme to treat your source water when starting a cycle.
I used it when I cycled (fishless, thanks to fishlore) my first tank last May. When it finally cycled, after the
water change, I used it with Stress-Coat and added the first fish (a female Betta), a couple of days later, I used it again when added a school of eight Zebra Danios.
Pepe
Santo Domingo