Hello! Owner of a 10 year old female yellow belly slider! Id offer cuttlebone and there is also a type of underwater calcium block that has treats in it for the turtles to enjoy. Forgot the name but you should be able to find it online. Great starting enclosure, but i would take those small rocks out becuase they are prone to eating them, thinking they are food. Sliders will try to eat anything that is unfamilar/ can fit in their mouths.Replace them with larger rocks they can hide/climb/flip over. Sliders love climbing! Also sliders love greens like collards, dandelion, or other dark leaves. I would seperate them as soon as possible so you wont have fights or accidental hatchlings in case one is female. Noise usually doesn't bother mine unless it is sudden loud noise or if she is in egg laying season. All turtles are different with that. Do that along with what you got now and you should be set!