Hanna and Extech make very good handheld TDS and pH meters. These are reasonably priced. The DO2 meters are a bit more expensive. Check the Internet for these two company products. I purchased mine from Granger Co. in the USA, but I’m sure you can get them in Oz.
Thank you Nick. I searched & was successful Hanna meters are available in Melbourne & they are sending me an email with costs. Thank you once again. I will buy you a beer when you get over here. Bob