The WQ-pH and the WQ-DO sensors may be connected to the same computer, but they most likely will interfer with one another, causing misreadings. There are two solutions to this problem:
1. Connect the sensors to two separate computers for the data.
2. Use isolated USB Hubs to separate the two sensors' grounds. Provided are two links to such USB Hubs.
http://www.sealevel.com/product_detail.asp?product_id=1216
http://www.bb-elec.com/product.asp?sku=uisohub4