Assuming the rock or sand is from an established tank (1 year plus), yes. I remember your other tank is new too so you might not get as much benefit. It will take weeks to properly cycle a tank with fresh dry rock and sand, but you can jump start things with established rock and sand. Go to High Tide Aquatics and buy some today if you can or see if Steve can sell you some from an established tank's sump since he's closing up shop soon.
The fact your pH is low and nitrites are high indicate something is decaying in there (old food, poop, etc.) and the nitrifying bacteria are struggling to keep up (that amount of animals in an 8g is high even when it's an established tank). Think of it like three people farting in an elevator with a broken air exchanger. The established rock is your air exchanger.
For the sake of your animals' well-being just trust us and read the articles about how long it takes to cycle a tank, we're trying to help!
