IMHO...that is the worst time to use nutrient rich water. You never know what is on the rock, ready to jump at you when it gets fed. Then again, I'll be the first to admit, that I'm "aways the newbie"
Each time I cycled my tanks (3 different tanks, not new cycles), I got hair algae, diatoms, and once, red slime. While cycling, the die off will cause enough nutrients to hit the water. This is what causes those pesky "new tank syndrome" blooms. If you add to that, with nutrient rich water, you could cause a big problem.