In my hydroponic system, I need to control the ph level with natural household items without harming the plants. Currently, the ph level is very low (3). Any one know how to do this both ways?
I very much doubt that your tap water and deep water culture have a pH of 3. Nutrient lockout occurs below 5.5 yet your plants mostly seem okay based on your previous question. City water tends not to be acidic as that would corrode pipes.
Furthermore as plants take up nutrients the pH tends to rise and as you add nutrients the pH falls. So one would expect your water to be alkaline.
In flood and drain systems the pH might be too high if you had grow media with too much calcium carbonate, or concrete tubs. So to raise the pH you could add dolmitic lime. Baking soda contains too much sodium which your plants won't like. Some people use sea shells, and egg shells to help buffer the pH.
Whether or not your household has any right now, probably the least likely to kill your plants common substance to raise pH would be ground limestone. In some systems limestone or marble chips are used, which last longer but act more slowly than the ground dust-like material.