@TopShelfAquatics pretty much nailed it. You have Cyano due to lack of flow.
I have a couple problems with air pumps and stones. Besides the aforementioned "salt creep", air pumps are loud and very prone to failure. Air stones clog in short order and need replacing. And most worrisome to me, I have read horror stories of air pumps failing and siphoning the tank all over the floor. The worst example of this was a pump that failed, back flowed water into the pump housing that started a fire and burned the house to the ground. A 1-way check valve would prevent this issue, but the others are inevitable.
For the plastic decorations, I agree that those plastics are not intended for saltwater. They become brittle and break apart, and can leach chemicals into the tank. Once you start adding corals, you will get the colors without the risks.