I just bought cycle by nutrafin an i was in the middle of cycling my tank will it stop the cycle or will help?

Also I got high ammonia in the beginning then 0 ammonia and high nitrites then 0 ammonia 0 nitrites then I got a low ammonia level and 0 nitrites what does this mean!!!Also any ideas on bringing pH down its at about 8.5 and my normal water is 7.5 there's nothing in the tank just normal aquarium gravel storebought driftwood and live plants.No seashells.I heard about that u could put peat mossin the filter bag but I dont understand how to do it.I want to keep tetras and platies and guppyies.Its a 29 gallon.Why is my tank recycling itself if thats what its doing I didnt add anything to the tank