Drinking water is Ph higher then we need so bring down the Ph is a must. Bottled water is better then boiling water. Letting it sit will not remove the chlorine and other minerals you don't want.

Could you put up a picture or a link so I know what system you are using? Flood and drain, drip, dwc or what type of hydroponics you have chosen, Iā??m not familiar with gro tank 205 model.